ENThe article is a continuation of author’s studies dealing with a role played by Radziwiłł princely family in Ukrainian history. As powerful magnates, Radziwiłłs had leading positions in Lithuania and Polish-Lithuanian Commonwealth. Some of them, being ardent Protestants, supported Orthodox clergy in the struggle against Union of Brest (1596) and maintained cultural and educational contacts with Kyivan literati. Along with these activities the paper examines some cultural endeavors of hetman Janusz Radziwiłł connected with his Kyivan campaign (1651). Special attention is paid to the reconstruction of castle in the city of Olyka which was Radziwiłłs’ residence for four centuries. The article contains also a brief review of recent historiography. It concludes with a call for the closer investigation of Radziwiłłs’ heritage in Ukraine.