Aim: The antioxidant efficacy of tender and mature coconut water of Cocos nucifera fruit was studied to ascertain the potential effects of the liquid on some biochemical indices. Materials and Methods: In vitro antioxidants activity was carried out on the coconut water using DPPH assay, ferric ion reducing antioxidant power assay (FRAP), and phosphomolybdenum assay (PM). Twenty albino rats (80 – 120 g) divided into 5 groups of 4 rats each were used for this study. Group 1 served as the normal control while groups 2-5 were induced with diabetes using 120 mg/kg b.w. alloxan monohydrate. Group 2 was untreated while Group 3 was treated with glibenclamide. Groups 4 and 5 were treated with 1 ml/kg b.w of mature coconut water and tender coconut water respectively. Results: Both tender and mature coconut water and that of the standard (ascorbic acid) showed a concentration-dependent DPPH scavenging capacity. The liquid also reduced the ferric ion in a concentration-dependent manner. Both tender and matured coconut water reduced Phosphate-Mo (VI) to Phosphate Mo (V) in a concentration-dependent manner. Malondialdehyde concentration (MDA) decreased significantly (p<0.05) when compared to group 2. The in vivo antioxidant status (CAT, GSH, Vitamin C, and Vitamin E) showed a significant (p<0.05) increase unlike group 2 while SOD activity showed significant (p < 0.05) increase in group 2. Conclusion: The results obtained from this study showed that both tender and mature coconut water have potent antioxidant properties and as such can reduce the complications associated with diabetes mellitus.