The paper presents the results of studying the cytotoxic activity of five new azolotriazine derivatives in order to establish the potential possibility of their use as antitumor agents, including two for breast cancer chemotherapy. The spectral characteristics confirmed high purity of obtained compounds and their stability on storage. The study determined cytotoxicity in the methyl tetrazolium test against MCF-7 and CHO cell lines The compounds were used at final concentrations from 0.25 to 10.0 mM/L. Two azolo[5,1-c][1,2,4]triazime derivatives (5a and 5d) had the calculated concentration of half-suppressed MCF-7 cell proliferation lower compared to the reference drug epirubicin. With respect to untransformed CHO cells, the cytotoxicity of all newly synthesized derivatives was lower than that of epirubicin, which further indicated the potential prospects of these compounds. The obtained data can be used as a basis for selecting compounds 5a and 5d for further study of their genotoxic and metabolic properties on cell models and laboratory animals, as substances with potential antitumor activity.