Mozhaysk (Можа́йск) is a town in Moscow Oblast, Russia, 110 km to the west from the Russian capital, on the historic road leading to Smolensk and then to Belarus. Its population is 20300.

New Mozhaysk cathedral was constructed in 1802-14.

The city is first mentioned in 1231 as an appanage of Chernigov. Later it was an important stronghold of the Smolensk dynasty, one time owned by Feodor the Black. The Muscovites seized it in 1303, but in the course of the following century had serious troubles defending it against Olgierd of Lithuania. The principality was usually held by a younger brother of the ruling Grand Duke of Moscow, until the practice was dropped in 1493. Mozhaysk continued to defend the Western approaches to Moscow during Napoleon's invasion of Russia and the Great Patriotic War. The great Battle of Borodino took place 12 km from the city.

The first stone cathedral was built in the kremlin at the turn of the 14th and 15th centuries; in 1849 it was demolished brick by brick and then reconstructed exactly as it used to be. A larger blood-red cathedral in the Gothic Revival style was completed in 1814. The church of St Joachim and Anna preserves some parts from the early 15th century. Another important landmark is the Luzhetsky monastery, founded in 1408 by Saint Ferapont and rebuilt in stone in the 16th century. The monastery cathedral, erected during the reign of Basil III, was formerly known for its frescoes, ascribed to Dionisy's circle.