Abstract: The use of mouthwash has increased because of attention to oral hygiene. Herbal mouthwashes have fewer side effects and are more economic than similar chemical drugs. In this study, the antimicrobial effects of ten herbal extracts on Streptococcus mutans were compared with chlorhexidine. Thirty grams of ten plants including thyme, mint, garlic, cinnamon, chamomile, tea tree, clove, spearmint, sage, and rosemary were dissolved in 100 mm of pure methanol and placed on a shaker for 48 h. Then, after passing the solution through a filter, they were put in an incubator at 37 centigrade degee for 48 h. Streptococcus mutans was cultured on blood agar. Chlorhexidine discs were used as positive controls while methanol and blank discs were used as negative controls. After 24 h the diameters of the halos indicative of lack of growth in each disc were measured with a pair of calipers. The zone diameters around each disc were compared with chlorhexidine using T test analysis. The inhibitory zone has observed around the Rosemary extract discs. Rosemary was found as a potent antimicrobial plant. More studies are suggested for production of herbal mouthwashes.