OBJECTIVE, MATERIAL AND METHODS: The aim of this study was to analyse the protein fractions of the soluble parasitic antigen (SPA) from in vitro cultures of the native Polish strains of Babesia canis canis and to determine their immunogenicity through Western blotting using the sera of dogs vaccinated with this antigen. Polyacrylamide gel electrophoresis revealed 21 protein fractions with molecular weights from 12 to 205 kDa. The most intense reaction in Western blotting was observed between the serum antibodies of the SPA-vaccinated dogs and the fraction with the molecular weight of 52 kDa. Detailed studies on the composition of SPA of Babesia canis canis and reactivity of its individual protein fractions can be a starting point for the development of subunit vaccines against babesiosis. Using a preparation with only some electrophoretic fractions of SPA in the production of vaccines would allow to avoid putting an unnecessary protein burden in the vaccine which could cause side effects.