Introduction: Dental caries and dental plaque are the most popular global oral health problems. The primary step of dental caries is characterized by damage of tooth surfaces  affected by acids which are by-products of sugar metabolism by a cariogenic bacteria. One of the cariogenic bacteria is Streptococcus mutans. Annona muricata is traditionally applied as an herbal remedy for various illnesses and has been recognized in a previous study as an antimicrobial agent. The aim of this study was to investigate  acid production and adhesion of ethanol extract of Soursop on Streptococcus mutans. Methods: Soursop leaf extracted by maceration using 70% ethanol solvent. The extracts obtained were tested at various concentrations. To examine the effect of ethanol extract of Soursop on acid production by S. mutans, the pH of the culture was determined using a pH meter. Inhibition of adhesion of S. mutans to the saliva-coated hydroxyapatite (S-HA) discs was quantified using colony counting on TYS20B agar plates. Results: The pH of S. mutans cultures in the presence of ethanol extract of Soursop leaf at various concentrations was higher than negative control, but there were no differences in pH value between the various concentrations of ethanol extract of Soursop leaf. Adhesion of S. mutans to S-HA discs was inhibited by various concentrations of ethanol extract of Soursop leaf. Adhesion decreased with increasing concentrations of ethanol extract of Soursop leaf, but there was not significant difference in colony count between the various concentrations of ethanol extract of Soursop leaf. Conclusions: Ethanol extract of Soursop leaf attenuates the acid production and adhesion of S. mutans to hydroxyapatite discs. Keywords: Soursop (Annona muricata); Streptococcus mutans; acid production; adhesion