The Mordovian Autonomous Soviet Socialist Republic (Russian: Мордовская Автономная Советская Социалистическая Республика, Mordovskaya Avtonomnaya Sovetskaya Sotsialisticheskaya Respublika; Erzya: Мордовскяй Автономнай Советскяй Социалистическяй Республикась, Mordovskjaj Avtonomnaj Sovetskjaj Socialističeskjaj Respublikaś; Moksha: Мордовской Автономной Советской Социалистической Республикась, Mordovskoj Avtonomnoj Sovetskoj Socialističeskoj Respublikaś) was an autonomous republic of the Russian SFSR within the Soviet Union.

It is now known as the Republic of Mordovia, a federal subject of Russia.

The Mordovian Autonomous Soviet Socialist Republic was established on December 20, 1934 by the transformation from Mordovian Autonomous Oblast [ru] of Kuybyshev Krai.

After Kuybyshev Krai was itself transformed into Kuybyshev Oblast, the Mordovian ASSR was separated from it and subordinated to the Russian Soviet Federative Socialist Republic.

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