Type 2 diabetes mellitus (T2D) is one of the most common endocrine diseases in the world. It is characterized by dysfunction of pancreatic β-cells, insulin resistance, and hyperglycemia. Despite numerous studies on the pathogenesis and risk factors of diabetes, there is still no consensus on how best to diagnose, classify, and treat the disease. Accumulating evidence suggests that antidiabetic drugs can course unwanted side effects. S-15176 difumarate salt, a novel derivative of trimetazidine, inhibits the rate-limiting enzyme of fatty acid β-oxidation carnitine palmitoyltransferase I and has anti-ischemic properties, which makes it useful as an antidiabetic agent. Here, the effect of chronic treatment with S-15176 difumarate salt on the leukocyte formula and cytochemical indices of the peripheral blood neutrophils (myeloperoxidase activity, free phospholipids, and lysosomal cationic proteins) of C57Bl/6 mice in control and experimental T2D was studied. It was found that in the control group, S-15176 difumarate salt decreased the number of neutrophils containing lysosomal cationic proteins and the cytochemical coefficient of the cells. The treatment of diabetic mice with S-15176 had no significant effect on the activity of myeloperoxidase and free phospholipids in neutrophils. The results obtained suggest that the use of S-15176 difumarate salt as an antidiabetic drug does not induce changes in peripheral blood markers associated with immune-related adverse effects.