マカオ返還（マカオへんかん）あるいはマカオ主権移譲（マカオしゅけんいじょう）は、1999年12月20日にマカオの主権がポルトガルから中華人民共和国に返還、移譲された出来事である。

マカオには明朝時代の1557年にポルトガル商人が入植し、程度の差こそあれ、マカオは1999年までポルトガルの支配下にあった。ポルトガルによるマカオへの関与は清朝により1749年に正式に認められている。ポルトガルの総督João Maria Ferreira do Amaralは、アヘン戦争の勝利と南京条約の締結の勢いのままに、清朝の現地当局を追放してマカオを併合しようとしたが、暗殺された。アロー戦争の終結後、1887年にポルトガル政府は、イギリス代表とともに、中葡和好通商条約を締結し、アヘン密輸を終わらせるための取り組みに協力するという条件でポルトガルによるマカオの永続領有が認められた。

1949年に中華人民共和国が成立し、1971年のアルバニア決議で国際連合の代表権が中華民国から中華人民共和国に移ると、当時の外交部長黄華が国際連合のに対してマカオ（と香港）を植民地一覧から除外するように求め、一覧への掲載により暗示された当地の独立ではなく主権返還に向けた二国間交渉の方が望ましいと発言した。

1974年4月25日、カーネーション革命でポルトガル軍の将校らが48年間続いた保守的な独裁政権エスタド・ノヴォを打倒し、新政府の下でポルトガルが民主主義に移行し、脱植民地化が行われることになり、1978年に中華人民共和国に対してマカオ返還を打診した。しかし、中華人民共和国政府は、マカオの早期返還は香港との関係に影響すると判断し、打診を拒否した。

1975年12月31日にマカオに残るポルトガル軍が撤退し、1979年2月8日にポルトガル政府は中華民国との断交を決定し、翌日に中華人民共和国との国交を開いた。その後、ポルトガル政府と中華人民共和国政府はともにマカオを中華人民共和国の領土と認め、1999年12月20日にマカオの主権が中華人民共和国に移譲され、マカオ特別行政区となり、約600年にわたるヨーロッパの植民地時代に終わりを告げた。

 交渉 
1986年5月20日、ポルトガル政府と中華人民共和国政府は6月30日にマカオに関する会談を北京で行うと正式に発表し、6月にポルトガル代表が北京を訪問すると、周南を始めとした中華人民共和国代表による歓迎を受けた。

北京における両国の会談は以下の4回に分けて行われた。
第1回：1986年6月30日 - 7月1日
第2回：1986年9月9日 - 10日
第3回：1986年10月21日 - 22日
第4回：1987年3月18日 - 23日

会談において、ポルトガルは1987年のマカオ返還を提案したとされるが、中華人民共和国は拒否し（過去にも1967年、1975年、1977年の要求を拒否していた）、代わりに香港返還と同年の1997年の返還を要求したが、ポルトガルが拒否した。その他、ポルトガルは2004年やマカオ租借450周年となる2007年を提案したものの、中華人民共和国は中英合同連絡グループが2000年に解散される予定のため、2000年以前の返還を主張し、最終的に1999年の返還で合意した。

1987年4月13日、マカオ問題に関する中葡共同声明がポルトガル政府と中華人民共和国政府により正式に発表され、北京において両国の首相が調印した。

 移行期間（1987年 - 1999年） 
が調印された1987年4月13日からマカオが返還された1999年12月20日までの12年間は、いわゆる移行期間とされていた。

1988年1月15日、中華人民共和国外交部は移行期間中にマカオ問題について協議するグループの構成員を発表し、4月13日にマカオ特別行政区基本法の起草委員会が全国人民代表大会で設立されると、10月25日に最初の委員会の会合で草案と起草段階の概要が採択され、マカオ特別行政区情報委員会基本法草案が設けられることが決まった。1993年3月31日、全国人民代表大会でマカオ基本法案が可決され、移行期間の後半の始まりとなった。

主権移譲

1999年12月19日、マカオ特別行政区の設立式典への前置きとして、ポルトガルの第127代マカオ総督ヴァスコ・ロシャ・ヴィエイラがマカオで旗を下ろした。正式な主権移譲はCultural Centre of Macau Gardenで同日夜に行われ、式典は夜に始まり12月20日の未明に終わった。

12月19日の夜は龍舞と獅子舞で始まり、マカオの歴史的出来事と特色のスライドショーが続き、これには東西の宗教と人種の混合とマカオで生まれたポルトガル人の特有の社会が含まれた。最後のパフォーマンスでは、マカオでのポルトガルの歴史442年を代表し、442人の子どもが、国際的なスターとともに「Praise for Peace」の歌を披露した。

余波
ポルトガルによるマカオの返還後、マカオ特別行政区、立法会、司法は基本法の規定に基づいて実施された。

Individual Visit Scheme政策の導入により中国本土の観光客の往来が容易になり、2005年だけでも本土から観光客1000万人が訪れ、これはマカオへの観光客の60%に相当する。マカオのカジノの収入は56億USドルに上る。2005年7月15日、マカオ歴史地区が世界文化遺産に登録された。観光業の発展がマカオ経済の急速な発展の主な要因になっている。

ポルトガルにとって、マカオ返還はポルトガル帝国、ポルトガルの脱植民地化だけでなく、中国大陸とアジアにおけるヨーロッパの帝国主義の終焉をも意味する出来事となった。

返還の前後
 変更されない（1999年12月20日以降） 変更された（1999年12月20日以降）Portuguese remains an official language. per Public signs are bilingual in Portuguese and Traditional Chinese, although signs may also include English. However, many schools teach in Cantonese in parallel with Mandarin and Portuguese.
The legal system remains separate from that of mainland China, broadly based on the Portuguese civil system, with some Portuguese judges continuing to serve.
Macau retained the pataca as its currency, which remained the responsibility of the Monetary Authority of Macau, and pegged to the Hong Kong dollar. However, the Bank of China began issuing banknotes in 1995.
The border with the mainland, while now known as the boundary, continues to be patrolled as before, with separate immigration and customs controls.
Macau citizens are still required to apply for a Mainland Travel Permit, in order to visit mainland China.
Citizens of mainland China still do not have the right of abode in Macau, except if he/she was born in Macau (before or after the establishment of the SAR). Instead, they had to apply for a permit to visit or settle in Macau from the PRC government. 
Macau continues to operate as a separate customs territory from mainland China.
It remains an individual member of various international organizations, such as APEC and WTO.
Macau continued to negotiate and maintain its own aviation bilateral treaties with foreign countries and territories. These include flights to Taiwan.
Macau remains an individual member of sporting organizations such as FIFA. However, the Sports and Olympic Committee of Macau, China, while a member of the Olympic Council of Asia, is not a member of the International Olympic Committee. 
It continues to drive on the left unlike Mainland China, all of which has driven on the right since 1946, or Portugal and most other Portuguese colonies, which switched to the right in 1928. Vehicle registration plates continued to follow the old Portuguese format, with white characters on a black plate. This had been discontinued in Portugal in 1992. 
Macau-registered vehicles can travel to and from mainland China, but require special cross-border plates, similar to those of Guangdong.
Macau citizens continue to have easier access to many countries, including those in Europe and North America, with Macau SAR passport holders having visa-free access to 117 other countries and territories. 
Foreign nationals, including Portuguese citizens, are allowed to hold high-level positions in the administration, except the office of Chief Executive; those who will apply for Chief Executive position will have to be naturalized as Chinese. This was in contrast to Hong Kong, where such positions were restricted to citizens of the SAR. 
Members of the existing Legislative Assembly, who had been elected in 1996, remained in office until 2001, although those who had been appointed by the Governor were replaced by those appointed by the incoming Chief Executive. 
Foreign nationals, including Portuguese citizens, are still allowed to stand for directly elected seats in the Legislative Assembly. This is in contrast to Hong Kong, where foreign nationals can only stand for indirectly elected seats in the Legislative Council. 
Macau continues to have more political freedoms than mainland China, with the holding of demonstrations and annual memorials to commemorate the Tiananmen Square protests of 1989 in Senado Square. However, pro-democracy politicians and academics from Hong Kong were refused entry.
It continues to have more freedom of the press than mainland China despite the growing influence of Beijing and Hong Kong journalists being refused entry.
Macau continues to have its own civic groups participating in the political system. These are separate from the Communist-led United Front on the mainland.
It also continues to have more religious freedoms, with the Roman Catholic Diocese of Macau remaining under the jurisdiction of the Holy See, instead of the Chinese Patriotic Catholic Association on the mainland. However, the Falun Gong spiritual practice has faced restrictions.
Macau retains a separate international dialling code and telephone numbering plan from that of the mainland. Calls between Macau and the mainland still require international dialling.
It retains different technical standards from mainland China, such as British-style electrical plugs. However, Macau would later adopt the digital TV standard devised in mainland China, instead of DVB-T, replacing PAL-I for TV transmissions.
Macau retains a separate ISO 3166 code, MO. It also retains a top-level domain, .mo. However, the Chinese code CN-92 was also used.
It retains its own separate postal services, with Correios de Macau operating separately from China Post. Macau was not made part of the Chinese postcode system, nor did it introduce a postcode system of its own.
Portuguese-influenced place names remain unchanged, although their unrelated Chinese equivalents are already in use; for example, Avenida Almeida Ribeiro is known as San Ma Lou or "new road".
Portuguese monuments remain, although the statue of former Governor João Maria Ferreira do Amaral was taken down in 1992. The statue is now located at the Bairro da Encarnação, Lisbon, Portugal, where it was placed in December 1999.
The floor on the ground level continues to be officially referred to by the Portuguese abbreviation R/C (rés-do-chão). The Chief Executive of Macau became the head of government, elected by a selection committee with 300 members, who mainly are elected from among professional sectors and business leaders in Macau. The Governor was appointed by Portugal.
The former Governor's Palace is now known as the Government Headquarters.
The Court of Final Appeal became the highest court of appeal in Macau. This replaced the Superior Court of Justice, established in April 1993. Appeals to the Court of Appeal of the Judiciary District of Lisbon ceased in 1999.
All public offices now fly the flags of the PRC and the Macau SAR. The Flag of Portugal now flies only outside the Portuguese Consulate-General and other Portuguese premises.
The People's Liberation Army established a garrison in Macau, the first military presence there since the Portuguese military garrison had been withdrawn following the Carnation Revolution in 1974.
The Central People's Government is now formally represented in Macau by a Liaison Office. This has been established in 1987 as a branch of Xinhua News Agency, when Macau was under Portuguese administration. Before 1987, it was informally represented by the Nanguang trading company.
The Macau SAR Government is now formally represented in Beijing by the Office of the Government of the Macau Special Administrative Region.
Elsewhere, the Macau SAR Government is now represented by Macau Economic and Trade Offices in Lisbon (Portugal), Brussels (European Union), Geneva (World Trade Organization) and Taipei (Taiwan).
The Ministry of Foreign Affairs of the People's Republic of China is represented in Macau by a Commissioner.
The Municipalities of Macau and the Ilhas, which had been retained provisionally following the transfer of sovereignty, were abolished and replaced by the Civic and Municipal Affairs Bureau with effect from 1 January 2002.
Portugal was now represented in Macau by the Portuguese Consulate-General, also accredited to Hong Kong. This had responsibility for matters relating to Portuguese nationals. However, residents of Macau born after 3 October 1981 were no longer entitled to Portuguese nationality.
The Taipei Trade and Tourism Office, the de facto mission of Taiwan, was renamed the Taipei Trade and Cultural Office, and was allowed to issue visas in 2002. It was later renamed the Taipei Economic and Cultural Office in Macau in 2011.
The words "República Portuguesa" no longer appear on postage stamps, which now display the words "Macau, China". The Portuguese coat of arms had already been removed from Macanese pataca banknotes and coins issued since 1988.
The Macau Police badge now displays the Macau SAR emblem.
The Portuguese honours system was replaced by a local system, with the Grand Medal of Lotus Flower as the highest award.
Public holidays changed, with Macau SAR Establishment Day being introduced and Portuguese-inspired occasions, such as Republic Day and Freedom Day, being abolished. PRC National Day had been made a public holiday in 1981.
Macau's aircraft registration prefix changed from Portugal's CS to B, as used by mainland China, Taiwan and Hong Kong.
The Portuguese national anthem A Portuguesa, is no longer played after closedown on television stations. The Chinese national anthem, March of the Volunteers, is now played instead.
A giant golden statue of a lotus, erected in a public space outside the Macau Forum named Lotus Square, was presented by the State Council of the People's Republic of China to commemorate the return of Macau to Chinese sovereignty.
The University of Macau was relocated to a new campus on Hengqin Island in 2009. This was under the jurisdiction of the Macau SAR government, which had leased a plot of land for M$1.2 billion until 2049.