Ukrainian Social Democratic Party (USDP) was a political party in Galicia. The party was founded in 1899 as an autonomous section of the Polish Social Democratic Party of Galicia (and Silesia) by some members of the Polish Social Democratic Party of Galicia (PPSD) and the Ukrainian Radical Party in Lviv. The key leaders were Mykola Hankevych (party chairman) and Semen Vityk. It was based on the Ukrainian social democratic organization that already existed since 1897. The first congress of the party took place in Lviv in 1903. Few years later in 1906 the party was joined by its affiliate in Bukovina, the Social Democratic Party of Bukovina (leader Yosyp Bezpalko).