The effect of the synthetic compound 2-morpholino-5-phenyl-6H-1,3,4-thiadiazine hydrobromide (L17) on rats with a streptozotocin-nicotinamide model of type 2 diabetes mellitus (DM2) was studied. The experiment was performed on 50 male Wistar rats; L17 was administered intramuscularly to diabetic rats at a dose of 40 mg/kg. When modeling DM2, hyperglycemia, accumulation of glycated hemoglobin (HbA1c) and MDA, a decrease in the content of thiols and compensatory activation of antioxidant defense enzymes (AOD) in erythrocytes (SOD, catalase, glutathione peroxidase) were revealed. Administration of L17 to diabetic rats was accompanied by a decrease in hyperglycemia, normalization of HbA1c and MDA levels, restored the activity of AOD enzymes, and, moreover, prevented the depletion of thiols. Correction of hyperglycemia and imbalance in the free radical oxidation-AOD system in the experiment makes further study of the mechanism of the antidiabetic action of L17 rather promising.