Introduction:Dental caries is one of the most prevalent disease worldwide. This disease caused by Streptococcus mutans. There are two methods to control Streptococcus mutans counts, which are mechanically and chemical-ly plaque control. One of chemically plaque control method used is Casein phosphopeptide-amorphous calcium phosphate (CPP-ACP). Topical application of CPP-ACP can inhibit the attachment of bacteria plaque on the teeth. It will inhibit the growth of Streptococcus mutans counts and prevent dental caries. Therefore, this study was to de-termine the effectiveness of CPP-ACP to increase the salivary acidity level and decrease the colony of Streptococcus mutans in children. Methods: This study was an experimental clinical study that aims to determine the impact of a treatment on research subjects. The design used in this study was pretest-posttest design. The participants were 30 children, aged 10-12 years old that obtained with purposive sampling. The saliva of the children were collect-ed before and after topical application CPP-ACP. The colony of Streptococcus mutans was determined by colony counting (Colony Forming Unit). The salivary acidity level was measured using dental saliva pH indicator. Results:This study showed that the mean of salivary acidity level before CPP-ACP topical application was 7.6333 and after CPP-ACP topical application becomes 7.7467. There was a significant difference in saliva pH level between before and after CPP-ACP topical application. The colony of Streptococcus mutans before CPP-ACP topical application was 4762,23±8104,682 CFU/ml and after CPP-ACP topical application was 555,73±409,602 CFU/ml. Wilcoxon test showed that there was a significant difference between the levels of salivary acidity and the colony of Streptococcus mutans before and after CPP-ACP topical application. Conclusion: There was an increase in the salivary acidity lev-els and decrease in the Streptococcus mutans counts before and after CPP-ACP topical application in the children.