The antileukemic activity of the original conjugate of anthracycline antitumor antibiotic epirubicin, covalently bond to the biopolymer chitosan was studied. The ascitic form of lymphocytic leukemia P388 (transplantation dose 1 x 106 tumor cells/mouse), in hybrid mice BDF1 was used as leukemic model. A strong antileukemic activity of the studied conjugate was found, with a clear “dose-effect” correlation. The criterion “increase of life span”(ILS%) reached maximally 553,4% for the conjugate, in comparison with maximally 170,8% for the free epirubicin. The conjugate showed several advantages over the free antitumor antibiotic epirubicin: lower toxicity, stronger antileukemic activity and higher therapeutic index.