Lubomirski's Rokosz, or Lubomirski's Rebellion (), was a rebellion against Polish King Jan II Kazimierz Vasa, initiated by the Polish nobleman, Jerzy Sebastian Lubomirski. In 1665-66, Lubomirski's supporters paralyzed the proceedings of the Sejm. Lubomirski himself, with the support of part of the army and the levee-en-masse (pospolite ruszenie), defeated royal forces, at Mątwy (1666). The rebellion ended with the Agreement of Łęgonice, which forced the King to give up his planned reforms and the introduction of vivente-rege royal elections. Lubomirski himself, now a broken man, died soon after.