By 1930, the Faculty of Physics and Mathematics had become a formal union of independent departments: mathematics, mechanics, astronomy-geodesy, physics, and geography (in 1929–1930, the State University Institute of Chemistry and the Faculty of Biology of Saint Petersburg State University [ru] had already separated from it).

In 1931,[1] the university's faculties were abolished and replaced by sectors: mathematics and mechanics, physics, geophysics, soil science and botany, physiology, and zoology.

In 1932–33, the sectors were transformed back into faculties: mathematics and mechanics, physics, biology, geology-soil-geography, and chemistry.

The first dean of the Faculty of Mathematics and Mechanics (technically, head of the corresponding sector) in 1931 was a postgraduate student of Grigorii Fikhtengol'ts, O.

In February 1942 Professor Nikolai Vladimirovich Roze [ru] was appointed dean but was arrested and repressed shortly thereafter.