Aims & Objectives: Ocimum sanctum L. popularly known as Tulsi is a medicinal plant that has been used for curing various diseases since ages. In the present study we used leaf extract of Ocimum sanctum for its anti-ulcer property by inducing stress ulcers on rats. Materials and Method: Albino rats were randomly allocated to different experimental groups and aqueous leaf extract of Ocimum sanctum was given for 7 days. Stress ulcers were induced by restraint and ethanol administered methods and results were compared with standard drug ranitidine. After that animal was sacrificed and stomach was dissected out and stomachs were observed for the ulceration with the help of magnifying lens and studied its external, internal surface and ulcer index was evaluated according to the severity of ulcers. The stomach were stored and fixed in 5% formalin and studied for histopathological changes. Results: The ulcer index was high in control group. Animal pretreated with Ocimum sanctum at the dose 100 & 200 mg/kg showed few signs of mucosal injury and the percentage of damage were less compared to control group. Conclusion: In the present study pretreatment with Ocimum sanctum at dose 100-200 mg/kg caused a significant anti-ulcer effect in rats in comparison with control group and its effect is comparable to the standard drug ranitidine, as evidenced by the reduction in the ulcer scores.