The Tosna (Russian: То́сна) is a northward river in Luzhsky, Tosnensky, and Kirovsky Districts of Leningrad Oblast, Russia, as well as in the city of Saint Petersburg.

The towns of Tosno, Nikolskoye, and Otradnoye, as well as the urban-type settlement of Ulyanovka are along it.

Its drainage basin covers 1,640 square kilometres (630 sq mi) which mainly has northward flowing streams.

In this area, limestone rocks occasionally form the banks.

A stretch of Tosna between Nikolskoye and Otradnoye serves as a border between the city of Saint Petersburg (west) and Leningrad Oblast (east).