In earlier experimental studies in vitro the Newcastle disease virus strain NDV/Altai/pigeon/770/2011 demonstrated significant cytolytic properties against various tumor cell lines, including colorectal cancer cells. It also inhibited the growth of various types of tumors in xenograft and syngeneic tumor models. The aim of the present study was to evaluate of the antitumor activity of several forms of NDV-containing drug on experimental adenocarcinoma CT26 and to compare the therapeutic effect with the classical cytostatic agent. Male BALB/c mice were used as model animals. Two experiments were conducted. In the first, intravenous antitumor therapy was started 48 hours after subcutaneous injection of CT26 tumor cells; in the second, therapy was started when the tumor reached a size of 150–400 mm³. A single injections of virus-containing drugs were administered for five days to mice from the experimental groups in each experiment: the unpurified form of the virus-containing drug and two purified forms of the virus-containing drug with the addition of hydroxyethyl starch and glucose. The mice in the control group were untreated. The comparison mice group was injected with cyclophosamide intraperitoneally (twice). According to the oncological parameters, therapy with an unpurified form of a virus-containing drug based on NDV strain proved to be effective, and the therapeutic effect was comparable in all major parameters with the group of animals receiving standard cyclophosphamide therapy.