ルーシ語
Unlike other Ruthenian magnates, the Ostrogskis refused to give up Eastern Orthodoxy for Roman Catholicism despite the cultural pressure that led to Polonization of Ruthenian nobility. For several generations the Ostrogskis supported the religion of their forefathers, by opening schools, printing books in Ruthenian language with Cyrillic such as "Ostrog Bible" (written by Ivan Fedorov) and making a generous charitable contributions to the construction of the Orthodox churches in the region.