Lomonosov (Russian: Ломоно́сов; before 1948: Oranienbaum, Ораниенба́ум) is a municipal town in Petrodvortsovy District of the federal city of Saint Petersburg, Russia, located on the southern coast of the Gulf of Finland, 40 kilometers (25 mi) west of Saint Petersburg proper.

Oranienbaum was granted town status in 1710, and was initially applied to the Oranienbaum palace complex, built between 1710 and 1725 opposite Kronstadt, in the neighbourhood of the royal residence Peterhof Palace, by the architects Giovanni Mario Fontana and Gottfried Johann Schadel, and was intended for Alexander Menshikov, a close associate of Peter the Great.

According to another version, the name means “Tree of Orange” in honour of William III of Orange, stadtholder of the Netherlands and king of England, who was the idol of Peter the Great, or it was borrowed from the toponymy of Germany (the city of Oranienbaum in the Principality of Anhalt named by Princess Henrietta Katharina Nassau-Oransky after her home place) simply as a “beautiful” name in the fashion spirit of the Petrine era.

An unofficial nickname, Rambov, a Russified contraction of the old name Oranienbaum, is popular among the local residents.

Lomonosov can be reached by suburban train from St. Petersburg's Baltic Terminal to Oranienbaum Station.