Ондрусовский монастырь, Orthodox monastery in Alavoine, Russia.

The Ondrusovsky Monastery stands on the eastern shore of Lake Ladoga, 25 km from Olonets. Its stone Church of the Presentation of the Virgin and Church of St Nicholas, both now ruined, survive along with the foundations of the monastery wall and towers and six residential buildings. The site occupies a peninsula near the mouth of the Alavoine River.

Adrian of Ondrusovo, a former nobleman who became a monk at Valaam, founded the hermitage at the mouth of the Olonka (Alavoine) river in the early 16th century; a church to St Nicholas was its first building. Tsar Ivan IV made donations, and Adrian died in 1549 on his way back from Moscow, killed by peasants. In 1572–1573 Swedish troops under Herman Fleming burned the wooden buildings; the monastery was abolished by Catherine II in 1764 and revived from 1817 with funds from Semyon Chusov and Andrey Sergeyev, attached to Valaam.

The name comes from the Karelian form Ontros of the founder's name Adrian. The monks spoke Karelian rather than Russian or Church Slavonic, which made them popular with the local population, and Karelians from Finland made pilgrimages here. The monastery kept old icons of Saint Paraskeva, of Sergius and Herman of Valaam, and a wonder-working icon of Saint Nicholas.

The monastery stands on the eastern shore of Lake Ladoga, about 25 km from Olonets; the ruins of the summer Presentation and winter St Nicholas churches, the foundations of the wall with towers and six residential buildings survive. The site is now used by the Mitrofanova Hermitage, so access should be arranged with that community rather than assumed.

The monastery is no longer active: it was closed after 1917, and its monks took refuge at Valaam Monastery in Finnish territory. Since 2011 the site has been leased to the Mitrofanije Hermitage. Ruins of the summer Presentation and winter St Nicholas churches, the foundations of the wall with towers and six residential buildings remain.