Prince Janusz Ostrogski (Lithuanian: Jonušas Ostrogiškis) (1554 – 17 September 1620 in Tarnów) was a Ruthenian noble and statesman of Polish–Lithuanian Commonwealth. He served as a voivode of Volhyn (1584-1593), as a castellan of Kraków (from 1593 on), and as a starosta of Bohuslav (from 1591), Biała Cerkiew (since 1592), Czerkasy and Kaniów (from 1594), Perejasław (1604 on) and Włodzimierz. Ostrogski was one of the richest magnates of the Commonwealth, and the last of the male line of his family. Upon his death his estate passed to the Zasławskis.