As a disease defined by the level of hyperglycemia, diabetes mellitus (DM) causes micro- and macrovascular damage. The present study evaluated the effect of methanol fraction of ethanol extract of Dialium guineense (MEDG) stem bark on cardiovascular disease risk factors in diabetic rats. Male Wistar rats (n = 25, mean weight = 215 ± 15 g) were used. The rats were divided into five groups (5 rats per group): normal control, diabetic control, metformin, MEDG (200 mg/kg body weight, bwt) and MEDG (300 mg/kg bwt) groups. Diabetes mellitus was induced via intraperitoneal injection of streptozotocin (STZ, 50 mg/kg bwt). The diabetic rats were then treated for 21 days with metformin (50 mg/kg bwt) or MEDG (200 and 300 mg/kg bwt, respectively). The results showed that STZ-induced DM significantly increased plasma concentrations of total cholesterol (TC), triacylglycerol (TG), very low-density lipoprotein cholesterol (VLDL-C), low-density lipoprotein cholesterol (LDL-C), atherogenic index of plasma (AIP), atherogenic coefficient (AC) and cardiac risk ratio (CRR), but it significantly reduced high-density lipoprotein cholesterol (HDL-C) (p < 0.05). However, treatment of diabetic rats with MEDG stem bark led to significant reductions in circulating levels of lipid profile (except HDL-C, which increased) as well as AIP, AC and CRR (p < 0.05). These results suggest that the medicinal plant extract has the capacity to protect against cardiovascular events in diabetic rats induced by STZ.