From ancient times, plants and plant-derived products have been used as folkloric medicines for a variety of health disorders owing to their tremendous therapeutic potential. The leaves of Acacia nilotica are widely used in the Indians traditional medicine to treat various types of diseases. The present study aimed to determine the antioxidant efficacy of crude Acacia nilotica leaf extract in the In vitro test system as Fenton reaction. The dried leaves of Acacia nilotica was extracted with methanol using a Soxhlet extractor. The total phenolics content of leaf as determined by Fenton reaction and was found to be good antioxidant activity as dose depended manner. The antioxidant activity of plant extract was carried out with ascorbic acid as a standard reducing agent. All the analysis was made with the use of UV-Visible Spectrophotometer. In this plant Acacia nilotica leaf extract there was a remarkable concentration dependent free radical scavenging and reducing power was exhibited. In conclusion the present study indicates that Acacia nilotica leaf extract may be a potential source of natural antioxidant. The results suggested that the studied leaves have strong antioxidant potential. Further studies are being carried out in order to provide complete data of the antioxidant activity and characterization of the principle antioxidant agents, which can be used to treat various oxidative stress-related diseases.