The article considers the peculiarities of the social-democratic views of the prominent statesman Simon Vasilyevich Petliura in the period 1902-1917, that is, at the stage of forming his political worldview. The role of S. Petliura as one of the leading ideologues of the Ukrainian social democracy of the beginning of the XX century is determined. The attitude of S. Petliura to the Russian variants of marxism is analyzed, his views on European social democracy, the main issues of development of the Ukrainian people, and solving them through the prism of socialist ideas. His views on party building are studied, relations between the Ukrainian Social Democratic Workers 'Party and the Russian Social Democratic Workers' Party. The key positions of the Russian Social Democrats have been identified, which became the subject of sharp criticism of S. Petliura. It turned out that Simon Petliura was a supporter of the European version of Social Democracy, in particular on the issue of the right of nations to selfdetermination. S. Petliura entered into a sharp controversy with representatives of the Russian Social-Democracy, argued the falsity of their views on non-recognition of the right of the Ukrainian people to autonomy, appealing to the works of Karl Kautsky. S. Petliura did not share the centralizing policy of the Russian Marxists regarding party building, defending the right of the Ukrainian Social Democratic Workers' Party to an independent organizational structure. Socialist ideology in views S. Petliura was dominant, but had bright national features. The key stages of formation of the worldview of the figure are determined. The transformation of its ideological foundations is determined.