The main target of hyperglycaemia is endothelial dysfunction involving pathways; protein kinase activation, hexosamine activation, polyol activation, and Advanced Glycation End Products (AGEs) formation, trigger reactive radical superoxide (O2•-) to stress oxidative. Malondialdehyde (MDA) is an end product of lipid peroxidation in body and is an indicator of oxidant-antioxidant level in diabetic patients. Fish oil composing mostly omega 3 as an antioxidant can reduce oxidative stress and hyperglycaemic condition. This study aimed to investigated the effects of omega-3-rich fish oil in lowering blood sugar levels, inhibiting oxidative stress and aortic endothelial cell damage in diabetic rat models. This study was an experimental study using post-test only control group design. Thirty-two rats divided into two study groups (n = 16 individuals per group), including the diabetic rat’s group (as control) and the diabetic rats group given fish oil doses of 300 mg/kilogram body weight/day. Provision of fish oil was performed for 28 days used Blackmores® fish oil. Blood sugar and malondialdehyde levels were analyzed by spectrophotometric method. The number of aortic endothelial cells was analyzed by haematoxylin-eosin staining. Comparability test showed that the average number of fasting blood glucose level after treatment in both groups showed highly significant differences (p=0.00). Although MDA level was reduced in treatment group than control group, but statistically not significantly difference, p=0.43. Comparability test showed that average of endothelial cell between control and treatment group significantly different (p=0.00). It was concluded that fish oil supplementation containing omega-3 in diabetic rats can lower blood glucose level and can inhibit endothelial cell damage.