The effect of Cola nitida consumption on melatonin production in albino male Wistar rats was investigated. Wistar rats weighing 150 – 220 g were fed for 30 days with different percentages of powdered Cola nitida (5%, 10%, 20%, 30% and 0% w/w). Serum concentrations of melatonin, ascorbic acid (AA), glutathione (GSH), serum alkaline phosphatase (ALP), serum aspartate aminotransferase (AST) and alanine aminotransferase (ALT) of albino rats were determined using standard methods. Results show that melatonin level increased in the range of 14.8-23.8 ng/ml. As the concentration of Cola nitida in the exposed groups increased there was a decrease in melatonin concentration (9.3 ng/ml). There was a significant decrease (p<0.05) in the level of ascorbic acid (0.0085 to 0.0057 mg/dl) and glutathione (5.7 to 2.5 mg/dl) compared to the control group which showed 8.9 mg/dl and 6.7 mg/dl respectively. Similarly, aspartate aminotransferase (56.7 to 24.8 U/l) and alkaline phosphatase activities (54.5 to 25.3 Ul) decreased significantly (p<0.05) as the concentration of Cola nitida increased compared to control. However, alanine aminotransferase activity increased as the concentrations of Cola nitida increased between 20% to 30%. This study shows that Cola nitida reduce the levels of melatonin production in exposed rats and may consequently cause sleeping related disorders among consumers or exposed groups.