The Siege of Bryansk Fortress occurred in November 1655 when Crimean Tatar forces loyal to Mehmed IV Giray captured Bryansk from forces loyal to his brother Islam III Giray amid the Crimean rebellion.
After the loss of Crimea, Yedisan, and Budjak to Mehmed Giray's rebels, Islam Giray's faction was confined to Bryansk, which the Tatar raiders had seized from the Tsardom of Russia. Jerzy Wisniewski led Mehmed Giray's armies north to Bryansk, which was defended by Islam Giray and nearly 500 of his loyal soldiers. Islam Giray gambled on a sortie that failed to push the besiegers back, and the besiegers proceeded to storm the fortress. The besiegers suffered significant losses during Bryansk's conquest, but they were able to overcome a larger army of less-experienced Crimean loyalists. Islam Giray was captured during the city's fall, severely weakening his faction.