This study deals with the activities of the Polish Socialist Worker's Party in the years 1921-1925, from the departure of a large number of its followers to the communists in 1921 to the Czechoslovak parliamentary election in November, 1925. The Polish socialists were in a very difficult situation, because they had to fight at the same time for the social interests of Polish workers, for the national interests of Polish minority, and against the communists. They cooperated with other parties of Polish minority in the fight for national rights, but they could not ignore the existing ideological differences. Polish socialists tried to cooperate with the Czechoslovak Social Democracy, too, but because there were great ethnical disputes between Czechs and Poles in the Teschen region of Silesia these efforts failed. At the parliamentary election in November 1925, Polish socialists approached, after a serious internal controversy, a coalition of other Polish parties.