Oxidative stress has recently been involved in the pathogenesis of type 2 diabetes mellitus. In a case-control study, we compared the serum homocysteine (HCY), vitamin B12 and folate levels as well as various oxidative stress biomarkers such as glutathione (GSH), total antioxidant capacity (TAC) and antioxidant enzymes (GPX, glutathione peroxidase, SOD, superoxide dismutase and CAT, catalase) in one hundred Omani subjects (50 type 2 diabetic patients and 50 age and gender matched controls). The levels of depression, anxiety and dietary intake of folate and vitamin B12 were also assessed. The results indicated that the retrospective dietary intake of folate and vitamin B12 in type-2 diabetic patients was significantly (P <0.05) lower as compared to controls and was even lower than the recommended dietary allowance (RDA). Low serum levels of folate and vitamin B12 were found to be closely associated with their low dietary intake. The mean serum HCY levels as well as the depression and anxiety scores were significantly (P <0.05) higher in type 2 diabetic patients as compared to controls. Oxidative stress was evident among type 2 diabetic patients as indicated by low serum levels of GSH, TAC, GPX, SOD and CAT as compared to controls. The results of this study suggest that the pathogenesis of depression and anxiety among type 2 diabetic Omani patients could be attributed to high serum level of HCY, low levels of dietary and serum folate and vitamin B12 and high levels of oxidative stress biomarkers.