There was investigated a new recombinant strain of Streptococcus pyogenes serotype M39, which did not express M-protein - "Gurov" emrrr. It revealed a higher antitumor activity towards transplantable solid murine tumors compared to wild type "Gurov". In a model of sygeneic transplantable hepatoma 22a we observed retardation of tumor growth and increase of survival after twice intratumoral injections of live S. pyogenes "Gurov" emm∼ as compared to a group of mice that received injections of S. pyogenes "Gurov" as well as to a control group of mice without treatment. In a model of transplantable Sarcoma 37 we also observed retardation of tumor growth after the introduction of mutant strain but without positive effect on survival. Additionally, it was showed that "Gurov" emm∼ strain possessed a higher direct cytotoxic effect towards hepatoma 22a cell line in vitro as compared to wild type "Gurov". Genetic modification of S. pyogenes "Gurov" strain attenuated its virulence and allowed to consider this strain as potent candidate for further studies and its possible application for oncolytic therapy in the future.