Inhibition of aerobic glycolysis of cancer cells is considered a promising therapeutic strategy for the treatment of neoplasms. Some inhibitors of energy metabolism can affect not only tumor cells but also the functional polarization of tumor-associated macrophages, which may either enhance the antitumor effect of such agents or impair their antitumor efficacy. To investigate the effect of oxamate, a lactate dehydrogenase (LDH) inhibitor, on the polarization of peritoneal macrophages (PMP) in both intact mice and mice with transplanted Lewis lung carcinoma (LLC). The low-metastatic LLC variant, LLC/R9, was transplanted to female C57Bl/6mice. Sodium oxamate was used as the test agent at concentrations of 0.02, 0.2, and 2mg/ml. Macrophage polarization in tumor-bearing mice was estimated on day 23after tumor transplantation by assessing nitric oxide (NO) production and arginase activity as functional indices of PMPs polarization. Oxamate can affect the functional polarization of PMPs in both intact mice and animals with transplanted LLC/R9. Oxamate in all studied concentrations changed the markers of PMPs polarization in intact mice (decreasing NO levels and activating arginase activity) that indicated the stimulation of M2polarization. In tumor-bearing animals, stimulation of M2polarization is observed at low concentrations of oxamate (0.02mg/ml), but its high concentrations (2.0mg/ml) causes M1polarization, which is characterized by three-fold increase in the level of NO and a decrease in the level of arginase activity. Oxamate, an inhibitor of LDH, can stimulate M2polarization of peritoneal macrophages of mice bearing LLC in a dose-dependent manner.