The article highlights the history of the so-called proletarian museums that opened in Moscow’s working-class suburbs in the 1920s. The study of their activities seems relevant, since it opens up the opportunity for a deeper study of the history of art museums in Moscow in the 1920s. Special attention is given to the Fifth Proletarian museum, which was a part of the State Tretyakov Gallery. More archival documents have survived on this museum than on any other of the proletarian museums. After studying some unpublished documents in Russia’s major archives, the author has discovered some important, previously unknown facts about these museums. This article takes a close look at how the paperwork was handled at the museum, how the items were registered, accounted for and taken care of and how the collections were accumulated and organized. Also thoroughly described in the article is the history of the museum’s closure as the author analyzes why it was eventually shut down. Moscow’s proletarian museums went down in history as an original new form of art institutions targeting “uncultured” visitors. Unfortunately, these museums were short-lived as they fell victim to the lack of funding and shortage of trained staff during the New Economic Policy era (1921–1928).