1936 Constitution of the Soviet Union followed by 1977 Soviet Constitution
The 1936 Constitution was the second constitution of the Soviet Union and replaced the 1924 Constitution, with 5 December being celebrated annually as Soviet Constitution Day from its adoption by the Congress of Soviets. This date was considered the "second foundational moment" of the USSR, after the October Revolution in 1917. The 1936 Constitution redesigned the government of the Soviet Union, nominally granted all manner of rights and freedoms, and spelled out a number of democratic procedures. The Congress of Soviets replaced itself with the Supreme Soviet, which amended the 1936 Constitution in 1944. 
The 1936 Constitution was the longest surviving constitution of the Soviet Union, and many Eastern Bloc countries later adopted constitutions that were closely modeled on it. It was replaced by the 1977 Constitution of the Soviet Union ("Brezhnev Constitution") on 7 October 1977.