Serpeysk (Russian: Серпейск, Polish: Sierpiejsk) is a village (selo) in Meshchovsky District of Kaluga Oblast, Russia, located on the Serpeyka River. It was first noted in 1406 as a military fort on the boundary between Muscovy and the Grand Duchy of Lithuania. During the 16th and 17th centuries, the town changed hands several times. It was definitively incorporated into Muscovite Russia after the signing of Treaty of Polyanovka which marked the end of the Smolensk War in 1634. Once stripped of its garrison, the town dwindled into oblivion. The oldest surviving buildings are two churches, one dating from 1771 and the other constructed in the 1780s.

Coordinates: 54°20′07″N 34°59′20″E / 54.33528°N 34.98889°E / 54.33528; 34.98889