Purpose The aim of study was to evaluate antibacterial effect of Rosemarinus officinalis extract on Streptococcus Mutans in group of Egyptian children in comparison with gold standard chlorhexidine. Subjects and Methods: Total of 40 Egyptian children with no sex predilection included in this study. Children's ages ranged from 6 to 12 years. Children divided into 2 groups A and B. Group A (experimental group): 20 children instructed to rinse with 5ml of R. officinalis extract twice per day for 2 weeks 30 seconds/rinse. Group B (control group): 20 children instructed to rinse with 5ml of Chlorhexidine (0.12 %) twice per day for 2 weeks 30 seconds/rinse. Results: In both groups there was statistically significant reduction in Streptococcus Mutans counts were obtained but the reduction was found slightly higher in chlorhexidine group. Conclusions: The use of Rosmarinus officinalis extract in children is safer than chlorhexidine because rosemary is natural herb that does not contain any chemicals.