Background: Increasing antibiotic resistance to pathogenic microorganisms (Streptococci) has led scientists around the world to turn to medicinal plants. In this study, the effects of aqueous and alcoholic extracts of Zataria multiflora on the in vitro growth of Streptococcus mutans and Streptococcus sanguis have been considered and compared with 0.2% chlorhexidine mouthwash. Materials and Methods: In this in vitro study, the inhibitory growth zone was accessed by the disc diffusion method after 48 h of incubation at 37 C. To find out the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of treatments, colony counts of cultured bacteria on nutrient agar have been considered at serial dilution at 1/2-1/1024 dilution rates. An independent t-test was used to compare the antibacterial effects of extracts while the level of significance of was considered to be 5% (P < 0.05). Results: The inhibitory growth zones of aqueous and alcoholic extracts on S. mutans were 26.8 mm and 35.8 mm, respectively, whereas growth zones for S. sanguis were considered as 25.8 mm and 33.2 mm, sequentially. Comparisons showed better effects of alcohol compared to aqueous extract (P > 0.05). The MIC and MBC assessments showed the same results (P > 0.05). In all comparisons, the effects of 0.2% chlorhexidine mouthwash were significantly better than both Z. multiflora aqueous and alcoholic extracts (P > 0.05). Conclusion: The different solvents may have contributed to the better effects of an alcoholic to aqueous extract of Z. multiflora on the growth of both bacteria. These two extracts could be used for early inhibition of the growth of the planktonic phase, as well as for better oral taste after chlorhexidine applications.