The Tikhvinka (Russian: Тихвинка) is a river in Boksitogorsky and Tikhvinsky Districts of Leningrad Oblast, Russia, a right and the biggest tributary of the Syas.

The source of the Tikhvinka is in Lake Yeglino in Boksitogorsky District, several kilometers northwest of the urban-type settlement of Yefimovsky.

The river flows northwest, through Lake Ozerskoye, turns west and eventually southwest.

Upstream of the village of Astrachi the Tikhvinka accepts the Ryadan from the left and turns west.

The whole course of the Tikhvinka is a part of the Tikhvinskaya water system, one of the waterways constructed in the early 19th century to connect the basins of the Volga and the Neva.