Konstanty Kazimierz Brzostowski (1644–1722) was a Polish noble, count of the Holy See, and papal prelate. He was Grand Secretary of Lithuania from 1671, and shortly thereafter was Grand Writer of Lithuania. He was bishop of Smoleńsk from 1685 to 1687 and bishop of Vilnius from 1687.
Brzostowski was a political opponent of the Sapieha family. In 1689 he was one of the judges who sentenced Kazimierz Łyszczyński to death for atheism. He unsuccessfully tried to make Peter I of Russia adopt more tolerant policies towards the followers of Union of Brest.