Background Cariogenic microorganisms are the most important cause for occurrence of dental caries. Dentifrices and mouthwashes containing antimicrobial substances are proven to be effective in the eradication of these pathogens from the oral cavity. Aim To evaluate the antimicrobial efficacy of fluoride, chlorhexidine (CHX), herbal, and xylitol containing toothpastes and mouthwashes against Streptococcus mutans (S. mutans) and Lactobacillus (LB) in subjects within the age group of 18 to 22 years at time intervals of 1, 3, and 6 months. Materials and methods One hundred subjects were randomly divided into four groups. Group I: fluoride, group II: chlorhexidine, group III: herbal, group IV: xylitol and instructed to use toothpastes and mouthwashes containing the specific agents. Salivary samples were collected to evaluate the levels of S. mutans and LB at baseline, 1, 3, and 6 months. Bacterial levels were evaluated using caries risk test (CRT) kit. Data were analyzed using analysis of variance and post hoc test. Results During intragroup comparison, S. mutans levels in group I showed statistically significant difference among the four time intervals. On intergroup comparison, S. mutans levels after 6 months for groups I, II, III, and IV were 1.12, 1.16, 1.28, and 1.4 respectively. Conclusion It can be concluded that fluoride, CHX, and xylitol showed a significant reduction in S. mutans and LB count after a time period of 6 months while herbal group did not show a significant reduction in S. mutans and LB count at any intervals. How to cite this article Sam JE, Benin P, Beaulah RH, Gnanaseelan, Krishna L, Raja J. Comparative Evaluation of Antibacterial Efficacy of Four Toothpastes and Mouthwashes against Streptococcus mutans and Lactobacillus: An in vivo Study. J Oper Dent Endod 2016;1(2):60-65.