Objective: To investigate the effect of Iranian honey, cinnamon and their combination against Streptococcus mutans bacteria.Methods: Nine experimental solutions were examined in this study, including two types of honey(pasteurized and sterilized), two types of cinnamon extract(dissolved in distilled water or dimethyl sulfoxide) and five different mixtures of cinnamon in honey(prepared by admixing 1%–5% w/w of cinnamon extract into 99%–95% w/w of honey, respectively).Meanwhile, each of mentioned agent was considered as the first solution while it was diluted into seven serially two-fold dilutions(from 1:2 to 1:128 v/v).Therefore, eight different concentrations of each agent were tested.The antibacterial tests were performed through blood agar well diffusion method, and the minimum inhibitory concentration(MIC) was determined.Ultimately, the data were subjected to statistical analysis incorporating Two-way ANOVA and Bonferroni post hoc tests(a = 0.01).Results: The highest zone of inhibition was recorded for the mixtures of honey and cinnamon while all the subgroups containing 95%–99% v/v of honey were in the same range(P < 0.01).The MIC for both honey solutions were obtained as 500 mg/mL whereas it was 50 mg/m L for both cinnamon solutions.Moreover, the MIC related to all honey/cinnamon mixtures were 200 mg/mL.Conclusions: A profound synergistic effect of honey and cinnamon was observed against Streptococcus mutans while there was no significant difference among extracts containing 99%–95% v/v of honey admixing with 1%–5% v/v of cinnamon, respectively. Objective: To investigate the effect of Iranian honey, cinnamon and their combination against Streptococcus mutans bacteria. Methods: Nine experimental solutions were examined in this study, including two types of honey (pasteurized and sterilized), two types of cinnamon extract (dissolved in distilled water or dimethyl sulfoxide) and five different mixtures of cinnamon in honey (prepared by admixing 1% -5% w / w of cinnamon extract into 99% -95% w / w of honey, respectively) considered as the first solution while it was diluted into seven serially two-fold dilutions (from 1: 2 to 1: 128 v / v). Therefore, eight different concentrations of each agent were tested.The antibacterial tests were performed through blood agar well diffusion method, and the minimum inhibitory concentration (MIC) was determined. Ultimately, the data were subjected to statistical analysis incorporating Two-way ANOVA and Bonferroni post hoc tests (a = 0.01). Results: The highest zone of inh ibition was recorded for the mixtures of honey and cinnamon while all the subgroups containing 95% -99% v / v of honey were in the same range (P <0.01). The MIC for both honey solutions were obtained as 500 mg / it was 50 mg / m L for both cinnamon solutions. More over, the MIC related to all honey / cinnamon mixtures were 200 mg / mL. Conclusions: A profound synergistic effect of honey and cinnamon was observed against Streptococcus mutans while there was no significant difference among extracts containing 99% -95% v / v of honey admixing with 1% -5% v / v of cinnamon, respectively.