Background. Erythrocyte metabolism is oxygen-independent and is enhanced under hyperglycaemic conditions due to increased glucose uptake. Cornelian cherry (Cornus mas L.) is a promising plant with diverse biological activities. This study aimed to investigate the effect of fruit extracts from different C. mas cultivars on the level of pyruvate (P), L‑lactate (L), their ratio (L/P) and the activity of lactate dehydrogenase (LDH) in the erythrocytes of diabetic rats. Methods. Diabetes mellitus (DM) was induced in rats by streptozotocin injection (55 mg/kg b.w.). Rats were divided into five groups (n = 8 in each group): 1) control rats; 2) rats with DM; 3) rats with DM treated with extract from fruits of the `Podolski´ cultivar of C. mas; 4) rats with DM treated with extract from fruits of the `Yantarnyi´ & `Flava´ cultivars of C. mas; 5) rats with DM treated with loganic acid — the main iridoid glycoside, extracted from fruits of C. mas `Yantarnyi´ & `Flava´. Extracts were administered per os once daily (20 mg/kg b.w.) for 14 days. The concentration of pyruvate and the activity of the LDH were determined according to the protocol of the analytical kits “Filicit-Diagnostics” (Dnipro, Ukraine) REF No. HP004.06 and REF No. HP015.01, respectively. The concentration of lactate was determined by an enzymatic-chemical method with the formation of Prussian blue. Statistical significance was assessed using one-way ANOVA and Dunnett’s post-hoc test (P < 0.05). Results. In erythrocytes of diabetic rats, the concentrations of pyruvate and lactate, the L/P ratio, and LDH activity increased by 1.3-, 2.9-, 2.3-, and 2.2-fold, respectively, compared with the control group. Treatment of diabetic rats with the extract from fruits of the `Podolski´ cultivar reduced pyruvate level by 15%, lactate concentration by 2.8-fold, the L/P ratio by 2.4-fold, and LDH activity by 2.1-fold compared with untreated diabetic rats. Administration of the fruit extract of the `Yantarnyi´ & `Flava´ cultivars to rats with DM decreased pyruvate concentration by 10%, lactate concentration by 2.3-fold, the L/P ratio by 2.0-fold, and LDH activity by 2.4-fold. Administration of loganic acid reduced pyruvate level by 20%, lactate concentration by 2.9-fold, the L/P ratio by 2.3-fold, and LDH activity by 3.4-fold, compared with untreated diabetic rats. Conclusions. Fruit extracts of C. mas improved glucose catabolism in erythrocytes of diabetic rats by normalizing pyruvate and lactate metabolism and reducing LDH activity, thereby alleviating diabetes-induced disturbances in carbohydrate energy metabolism.