The synthesis of several new 3-substituted aminopyrazolo[3,4-b]pyridines is described. The obtained compounds were tested for their antiproliferative activity in vitro. Two of them: 3-chloroacetylaminopyrazolo[3,4-b]pyridine [II] and 3-(2-bromopropionyl-amino)pyrazolo[3.4-b]pyridine [III] revealed cytotoxic activity against the cells of 5 human tumor cell lines applied. Their ID50 values were in the range of the international activity criterion for synthetic agents (4 microg/ml). The structures of the products II-XVII were established on the basis of elemental analysis and spectral data (IR, 1H NMR and MS).