The article is devoted to enlighten the relative and politic contacts on Radzivills towards the heritage of the Sobieskis. All events concerning this theme began with the marriage of Katarzyna Sobieska. She got married with Władysław Dominik Zasławski-Ostrogski in 1650. They had two children Aleksander Janusz who died young and with no children and Teofila Ludwika. We have no information about a dowry which Katarzyna should have got. Soon she was widowed by her twenty years older husband and in 1658 she got married to Michał Kazimierz Radziwiłł. His brother-in-law Jan Sobieski became the voivode of Vilnius and high-standing person of the Great Duchy of Lithuania.