ウィリアム・ヘムズリー（William Botting Hemsley、1843年12月29日 - 1924年10月7日）はイギリスの植物学者である。王立植物園（キューガーデン）で働いた。

サセックスのイースト・ホースリーで生まれた。1860年からキューガーデンで働き、1889年に王立協会のフェローに選ばれた。トーマス・チーズマン（Thomas Frederick Cheeseman）と共著の、『ニュージーランドの植物の図説』（Illustrations of the New Zealand flora）やダニエル・オリバー（Daniel Oliver）の『熱帯アフリカの植物』の"Rhamneae"（クロウメモドキ連）や"Campanulaceae" （キキョウ科）、 "Scrophulariaceae" （ゴマノハグサ科）、"Balanophorsceae"（ツチトリモチ科）などの章を執筆した。

ウリ科の属名ヘムスレイア属 Hemsleyaに献名されている。

著書 
 "Report on the scientific results of the voyage of H.M.S. Challenger during the years 1873-1876" ; Botany ; vol. 1, pt. 3, London, Edinburgh, Dublin, [1884]-1885. 
ウィキスピーシーズの記事。
マイクロフィッシュ版。 Report on the botany of Juan Fernandez, ..., IDC Publishers, .  IDC order no. 110.
タイトル別名 Report on the botany of Juan Fernandez : the south-eastern Moluccas, and the Admirality Islands ; Report on the scientific results of the voyage of H.M.S. Challenger during the years 1873-1876
(Linden, Jean Jules、André, Edouard François 編) The illustration horticole : an illustrated monthly review of new and interesting plants with their descriptions, history and culture, [s.n.]. 1874, .
 Diagnoses Plantarum Novarum (1878–1880)　ウィキスピーシーズの記事。

共著 
 Biologia Centrali-americana … Botany (5巻), 1879–1888, (online)
 Botany, Published for the editors by R. H. Porter and Dulau. 1879. 〈Biologia Centrali-Americana〉 / F. Ducane Godman、Osbert Salvin 編, . (Hooker, Joseph Dalton, Sir、Thiselton-Dyer, William T. (William Turner) と共著)

 Handbook of hardy trees, shrubs, and herbaceous plants : containing descriptions, native countries, etc. of a selection of the best species in cultivation, together with cultural details, comparative hardiness, suitability for particular positions, etc. : based on the French work of Messrs. Decaisne and Naudin entitled 'Manuel de l'amateur des jardins,' and including the original woodcuts by Riocreux and Leblanc, Estes & Lauriat. 1873, . (Decaisne, Joseph、Naudin, Charles、Rand, Edward Sprague と共著) 
 Handbook of hardy trees, shrubs, and herbaceous plants : containing descriptions, native countries, etc. of a selection of the best species in cultivation, together with cultural details, comparative hardiness, suitability for different situations, etc. : based on the French work of Messrs. Decaisne and Naudin entitled "Manuel de l'amateur des jardins" and including the original woodcuts by Riocreux and Leblanc, Longmans, Green. 1877, . (Decaisne, Joseph、Naudin, Charles と共著) 
 Enumeration of all Plants known from China, 1886、1895. (Francis Blackwell Forbesと 共著)
 Illustrations of the New Zealand flora, John Mackay, 1914, .  (Cheeseman, T. F. (Thomas Frederick)、Smith, Matilda と共著)
 Flora Simlensis : a handbook of the flowering plants of Simla and the neighbourhood, Thacker, 1921, .  (Collett, Henry と共著)
 Flora Simlensis : a handbook of the flowering plants of Simla and the neighbourhood, Bishen Singh Mahendra Pal Singh. 1980, .  (Collett, Henry と共著)
 A sketch of the vegetation of British Baluchistan with descriptions of new species. Bishen Singh Mahendra Pal Singh, 1978, . (Lace, J. H. (John Henry) と共著)
 Collection of plants from Upper Burma and the Shan states, Bishen Singh Mahendra Pal Singh.  1979, .  (Collett, Henry と共著)
 An enumeration of all the plants known from China Proper, Formosa, Hainan, Corea, the Luchu Archipelago, and the Island of Hongkong : together with their distribution and synonymy, O. Koeltz Science Publications, 1980, , .  (Forbes, Francis Blackwell と共著)