BACKGROUND Fixed orthodontic appliances predispose patients to dental caries. Use of mouthrinses has been introduced as the effective way for reducing dental plaque accumulation. OBJECTIVE The aim of this study was to compare the effects of Persica mouthwash and Chlorhexidine (CHX) on colonization of Streptococcus mutans (S. mutans) on fixed orthodontic O-rings. METHODS Thirty patients with fixed orthodontic appliances and proper oral hygiene were randomly provided by CHX and Persica and trained to use these mouthwashes according to the manufacturer's instruction. Sampling was carried out right before and 4 weeks after mouthrinsing treatment. The mean amounts of S. mutans colonies in these groups were compared. RESULTS Comparison of S. mutans colonization within each group revealed both mouthrinses to be efficient. However, this difference was found to be significant only in CHX group. CONCLUSIONS Persica cannot be a good alternative mouthwash and patients on orthodontic treatment are still recommended to use CHX.