Konstanty Wasyl Ostrogski (Ukrainian: Костянтин-Василь Острозький, romanized: Kostiantyn-Vasyl Ostrozkyi; Belarusian: Канстантын Васіль Астрожскi; Lithuanian: Konstantinas Vasilijus Ostrogiškis; 2 February 1526 – 13 or 23 February 1608) was a Ruthenian Orthodox magnate of the Polish–Lithuanian Commonwealth, a prince, starost of Volodymyr, marshal of Volhynia and voivode of the Kiev Voivodeship.

In the 1570s he waged a war against another magnate, Stanisław Tarnowski, about disputed possession of estates in the area of Tarnów, in Lesser Poland.

Around 1576[3] he established the Ostroh Academy, a wellregarded humanist educational and scholarship institution, with the instruction in Greek, Latin and Old Church Slavonic languages.

Ostrogski's huge latifundium, or landed estate in the eastern Polish–Lithuanian Commonwealth, consisted of 100 towns and 1300 villages.

Ostroh boasted an Orthodox academy, a yeshiva, a mosque, and a Unitarian Church.