Diabetes mellitus is accompanied by metabolic and oxidative stress-related complications and supportive treatment with natural products might prevent or delay the progression of these complications. The present study hypothesized that Brassica nigra pollen (BNP), shown to have metabolic and antioxidative properties, can reduce oxidative stress and genotoxicity and improve metabolic parameters in diabetes mellitus. Diabetes was induced by intraperitoneal injection of STZ (65 mg/kg). The rats were divided into four groups; control rats; control group rats given BNP; diabetic rats; diabetic group rats given BNP. Rats were given with BNP for thirty days (350 mg/kg/day). Serum insulin, blood glucose, triglyceride, total cholesterol, high-density lipoprotein-cholesterol, alanine aminotransferase, aspartate aminotransferase levels were evaluated using an auto-analyzer. Plasma and tissue malondialdehyde (MDA) levels were measured with spectrophotometric methods. Serum paraoxonase (PON), arylesterase (ARE), superoxide dismutase, glutathione peroxidase activities were determined using commercial kits. Genotoxicity was determined by the bone marrow micronucleus (MN) method. BNP recovered the increased plasma and heart, muscle, liver, and kidney tissue MDA and serum glucose and total cholesterol levels. BNP increased serum PON, ARE activities and showed antigenotoxic activity by decreasing MN frequency in the BNP-treated diabetic rats. BNP has antihyperglycemic, antihyperlipidemic, antioxidant, and antigenotoxic properties and can be a promising supportive therapeutic agent in diabetes mellitus for improving treatment outcomes and reducing treatment-related and/or diabetes-related complications.