This study aimed to measure the effect of xylitol mouthrinse on salivary Streptococcus mutans counts.Subjects in the study group (n = 25) used xylitol mouthrinse for 4 weeks, while another group (n = 25) used saccharine mouthrinse. S. mutans were measured before and after intervention.At the baseline the mean S. mutans scores were 3.9 (SE = 0.03) and 3.9 (0.04) for the xylitol group and control group respectively, while the scores were 2.8 (0.13) and 3.9 (0.07) after the intervention. Significant reductions (p < 0.01) in the scores of S. mutans were found after the four week use of xylitol mouthrinse.Significant reductions in the scores of S. mutans were found after the four week use of 20% xylitol mouthrinse. The bacteriostatic effect of xylitol mouthrinse on S. mutans may be comparable to other xylitol products. Further studies are needed to confirm both the short and long term effects of xylitol mouthrinse.