The aim of the present study is to determine the anti-diabetic efficacy of the methanolic extracts of the rind ofCitrullus lanatus (watermelon) in alloxan induced diabetes in male albino Wistar rats. Thirty five rats weighing between 180g and 250 g were randomly assigned to seven groups: 1 to 7. Diabetes was induced in all the rats except Group 1 by intraperitoneal injection of 150mg/kg bw of alloxan. Group 1 rats served as positive control and received 2ml/kg bw of extract vehicle; Group 2 rats served as negative controls: untreated diabetic group; Groups 3, 4 and 5 rats received 100mg/kg bw, 200mg/kg bw and 500mg/kg bw of the methanolic extract of the rind of Citrullus lanatus respectively; while Group 6 received 600µg/kg bw of oral glibenclamide, and Group 7 received (10iu/kg) of subcutaneous insulin. The drugs and extracts were administered orally via oral canula for 30days. On day 31, blood samples were collected from anaesthetized rats using chloroform by cardiac puncture for biochemical and hematological assays. Results obtained showed that at different doses, the extract of Citrullus lanatus increased both food intake and body weight but decreased water intake in Groups 3, 4 and 5 rats compared to Group 2 rats (p<0.05). Furthermore, significant decreases were seen in the levels of triglycerides, low density lipoprotein-cholesterol, very low density lipoprotein-cholesterol; with increases in high density lipoprotein-cholesterol in Groups 4 and 5 only compared to Group 2 rats (p<0.05). Treatment with the extract caused significantly lowering of the levels of urea and creatinine in Groups 3, 4 and 5 rats compared with Group 2 rats (p<0.05). There was significant decrease in the levels of aspartate aminotransferase, alanine aminotransferase, alkaline phosphatase and glycosylated hemoglobin in rats of Groups 3, 4 and 5 compared to Group 2 rats (p<0.05). These results obtained from the extract groups were fairly similar to that obtained for rats in Groups 6 and 7 treated with standard anti-diabetic agents. These results suggest the possibility that the methanolic extract of the rind of Citrullus lanatus could help normalize some biochemical and hematological abnormalities associated with the pathophysiology of diabetes mellitus in a dose dependent manner.