Background:The aim of the present study was to compare the antibacterial effects of coffee extract with those of 0.2% sodium fluoride and chlorhexidine (CHX) mouthrinses on Streptococcus mutans and Lactobacillus plantarum in vitro.Materials and Methods:In this experimental in vitro study, the minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC), and disk diffusion method were determined for different concentrations of coffee extract, 0.2% CHX, and 0.2% fluoride against S. mutans and L. plantrum. Data were analyzed using Kruskal–Wallis analysis. Statistical significance level was established at P < 0.05.Results:The MIC of coffee was achieved at 62.5 and 500 mg/mL against S. mutans and L. plantarum, respectively. The MBC against S. mutans was 125 mg/mL. The diameter of the zone of inhibition around S. mutans for pure coffee extract (100%), CHX (0.2%), and fluoride was 19.8 mm, 9.92 mm, and 0, respectively. At a concentration of 6.25%–100%, coffee had a significantly larger zone of inhibition compared to CHX and fluoride) P = 0.01). The MBC of coffee and fluoride was 0 against L. plantarum. The lowest inhibitory concentration belongs to CHX (MIC: 0.624 mg/ml for L. plantarum and 0.125 mg/ml for S. mutans).Conclusion:The coffee had an antibacterial effect against S. mutans on 62.5–1000 mg/ml concentrations. The zone of inhibition around S. mutans for higher concentrations of coffee (6.25%–100%) was significantly higher than that of CHX and fluoride 0.2%. Bacteriostatic effect of coffee against L. plantarum was obtained at 500–1000 mg/ml. However, coffee and fluoride did not show any bactericidal effects against L. plantarum.