Objective To explore the relationship of the serum level of omentin with oxidative stress in the elderly diabetic patients with hypertension. Methods A total of 127 elderly patients with type 2 diabetes mellitus (T2DM) in our department from June 2015 to December 2016 were recruited in this study. According to the complication of hypertension, they were divided into T2DM with hypertension group (n=69, hypertension group) and T2DM with normal blood pressure group (n=58, non-hypertension group). Another 30 healthy elderly individuals who taking physical examination in our hospital during the same period served as the control group. The serum levels of omentin, malondialdehyde (MDA), superoxide dismutase (SOD), and glutathione peroxidase (GSH-px) were measured in the 3 groups. SPSS statistics 20.0 was used for statistical analysis, and Students’ t test was employed for the measurement data. Pearson linear correlation analysis was performed to test the relationship of the serum level of omentin with that of MDA, SOD and GSH-px in the elderly diabetic patients with hypertension. Results Before the treatment, the serum omentin, SOD, and GSH-px levels were significantly lower, while that of MDA level was obviously higher in the hypertension group than in the non-hypertension group (P<0.01). After the treatment, the hypertension group had the levels of omentin, SOD, and GSH-px notably increased, but those of MDA and MAP declined (P<0.01). In the diabetic patients with hypertension, their serum omentin level was negatively correlated with serum MDA (r=-0.587, P＜0.01) and MAP (r=-0.542, P＜0.01), and positively correlated with the serum levels of SOD (r=0.683, P＜0.01) and GSH-px (r=0.596, P＜0.01). Conclusion The decline of serum omentin level increases oxidative stress, and this may be one of important pathogenetic mechanisms of hypertension in the elderly diabetic patients.