Abstract: Caffeine is the most widely used natural stimulant, found in beverages, medicine and some popular masticatories. The aim of this study was to investigate the effects of prolonged oral administration of caffeine on hepatorenal functions of male Wistar rats. In this study 32 Wistar rats (120g-240g) were used. The animals were divided into four groups of 8 rats each with group 1 as control given only feed and water. Group two were given 2mg/kg caffeine, group 3 given 4mg/kg caffeine and group 4 given 6mg/kg caffeine orally for 28 days. The result showed significant decrease in body weight. There was also a statistically significant increase in the concentrations of urea, creatinine, uric acid, bicarbonate and chloride in groups 3 and 4 and a statistically significant decrease in the concentrations of potassium and sodium in groups 3 and 4.