In the 1960s, when the Second Vatican Council and the Moscow Patriarchate invited Christian churches to develop closer ecumenical relationships, the first signs of ecumenism appeared in Lithuania. In 1965, the first ecumenical service was held in the Šilutė Lutheran Church, which was attended by representatives of four denominations. Such ecumenical relations soon became a common phenomenon in Soviet Lithuania. The article analyzes the origins of the ecumenical movement and its development in Lithuania, as well as the reaction of the Commissioner of the Council of Religious Affairs in Moscow for Lithuania to this new religious phenomenon.