Aim. A comparative analysis of the anti-cancer activity of 1-(4-methylpiperazin-1-yl)isoquinolines with different heteroaromatic substituents in C-3 position: 2-methylthiazol-4-yl, 2-phenylthiazol-4-yl, 2-(pyridin-4-yl)thiazol-4-yl, imi-dazo[2,1-b]thiazol-6-yl, quinoxalin-2-yl, 6,7-dimethylquinoxalin-2-yl. Methods. Biological tests; statistic methods. Results. In vitro screening of the anticancer activity showed that the derivatives with 2-phenylthiazol-4-yl, quinoxaline-2-yl, 6,7-dimethylquinoxalin-2-yl substituents demonstrated the highest level of anticancer activity; however, they were inferior to 2-(pyridin-4-yl)thiazol-4-yl. The product with the 2-methylthiazol-4-yl residue almost did not demonstrated cytotoxicity. Comparative analysis showed no significant correlation with known drugs; hence these compounds have specific molecular targets. Conclusions. The resulting 1-amino-3-hetarylisoquinolines are a promising class of compounds for anticancer drug development. The level and direction of the activity significantly depend on the nature of heterocyclic substituents.