Aim: To determine the number of colony forming units of Streptococcus mutans and Lactobacillus acidophilus present in human dental plaque before and after chewing fresh Ocimum basilicum leaves. Material and Method: 15 female school children, aged 14-15 years, were selected from a high school using convenience sampling technique. Baseline plaque sample was collected using plaque harvesting technique from the buccal surfaces of posterior teeth. Subjects were asked to chew 10 fresh Krishna Tulsi leaves for 1 minu te everyday for 15 days. After this, a second plaque sample was collected using the same technique. The microorganisms were cultured from both the plaque samples in their respective culture media. The colony forming units were counted and compared between the pre intervention and post intervention samples. Student′s paired′t′ test was carried out. Results: There was a statistically significant decrease in the Streptococcus mutans count after chewing Tulsi leaves. There was a numerical decrease in the Lactobacillus acidophilus count after chewing Tulsi leaves, but the difference was not statistically significant. Conclusions : Chewing fresh Krishna Tulsi leaves reduced Streptcoccus mutans and Lactobacillus acidophilus colony count in human dental plaque.