Given the prevalence of diabetes worldwide, with its associated complications, this study is aimed at investigating the effect of citrullus lanatus seed extract on blood glucose concentration and electrolyte parameters. Citrullus lanatus is an antioxidant and has been shown to reduce oxidative stress (Khaki et al., 2013). Effects of phytochemicals (flavonoids) on pancreatic β-cells leading to their proliferation and secretion of more insulin have been proposed by Mahesh and Menon (2004), as the mechanism by which medicinal plants used in the treatment of diabetes mellitus reduce hyperglycaemia in streptozotocin-induced diabetic rats. Fifteen female wistar rats were used in the study, they were divided into three groups of five rats each, namely; the control group, diabetes control group administered distilled water, and diabetes group administered watermelon seed extract. The diabetic groups were made diabetic by single intraperitoneal injection of streptozotocin (60 mg/kg). Daily watermelon seed extract was administered orally (200 mg per kilogram body weight), one week post streptozotocin injection. On 29th day the rats were sacrificed and blood was collected via the inferior vena cava, into plain bottles and fluoride oxalate sample tubes for electrolyte; (Na+, K+, HCO3-, Cl-) and glucose analyses, respectively. Results showed that plasma glucose concentration decreased significantly (P<0.05) at week 2 and 4. However, administration of methanolic extract of Citrullus lanatus seed did not have any significant effects (P>0.05) on Na+, K+ , Cl- , and HCO3- concentrations . In conclusion, watermelon seed extract may be of supportive treatment to combat diabetes complications.