The Kirov Plant or Kirov Factory (Кировский Завод, Kirovskiy Zavod) is a major Russian machine-building plant in St. Petersburg, Russia.

It was established in the 1800s as a cannon ball foundry. In 1848 it was purchased by Putilov and named the Putilov Company; it initially produced rolling stock for railways. It boomed during the industrialization of the 1890s, with the work force quadrupling in a decade, reaching 12,400 in 1900. The factory traditionally produced goods for the Russian government and railway products accounted for more than half of its total output. Starting in 1900 it also produced artillery, eventually becoming a major supplier of it to the Imperial Russian Army alongside the state arsenals. By 1917 it grew into a giant enterprise that was by far the largest in the city of St. Petersburg. In February 1917 strikes at the factory contributed to setting in motion the chain of events which led to the February Revolution.

After the October Revolution it was renamed Red Putilovite Plant (zavod Krasny Putilovets), famous for its manufacture of the first Soviet tractors, Fordzon-Putilovets, based on Ford's Fordson tractor. The Putilov Plant was famous because of its revolutionary traditions. In the wake of Sergey Kirov's 1934 assassination, the plant was renamed Kirov Factory No. 100.

The Kirov Plant is sometimes confused with another Leningrad heavy weapons manufactory, Factory No. 185 (S.M. Kirov).