Rumer returned to Moscow in May 1932, as persecution of Jews in Germany became a real threat to him and his wife. He became an associate professor at the Faculty of Physics of Moscow State University (MSU) and assumed a professor position in January 1933. He was recommended for this position by Erwin Schrödinger and Leonid Mandelstam. At MSU Rumer supervised several notable scientists, including Mikhail Volkenshtein. He lectured at MSU from 1932 to 1937 and worked as a scientist at the Lebedev Physical Institute from 1935 to 1938. In 1935 he defended his habilitation, and in 1937 started working with Lev Landau ; very soon they became close friends.