Purpose: The oral cavity is a rich ecosystem with a plethora of microorganisms, and different components of fixed orthodontic appliances may contribute to a shift in the balance of oral ecology. The purpose of this study was to investigate the antimicrobial potential of hexane and ethanol extracts of Salvadora persica on a monospecies biofilm model established on orthodontic brackets in vitro. Materials and Methods: Streptococcus mutans biofilm was formed on mini diamond orthodontic brackets following three days of anaerobic incubation at 37˚C. The bacterial cell viability of this biofilm was measured after their exposure to saline, hexane extract of S. persica, ethanol extract of S. persica and 0.2% chlorhexidine using 3-(4, 5-dimethylthiazol- 2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulphophenyl)-2H-tetrazolium (MTS) assay. On half of the brackets, the colony forming units (CFU) were counted. Both experiments were performed in triplicate. Results: The absorbance values obtained from the MTS reduction assay after exposure to the different test agents showed a decline in the bacterial cell viability of the S. mutans biofilm as follows: chlorhexidine (+) hexane extract (S. persica, 5 mg/ml) ethanol extract (S. persica, 5 mg/ml) saline + 2% DMSO (-). There was significant difference between saline + 2% DMSO and the other test solutions (p 0.05). The mean absorbance values showed that the antimicrobial activity of hexane extract was slightly more effective than that of the ethanol extract and was nearly as effective as chlorhexidine (+). However, the differences in the absorbance values between the extracts of S. persica and chlorhexidine (+) were not statistically significant (p > 0.05). The CFU counts of S. mutans obtained from chlorhexidine exposure were lower than from hexane and ethanol extracts. Conclusion: S. persica extracts were found to have antimicrobial effects on S. mutans biofilm established in vitro on orthodontic brackets suggestive of its potential use as an oral antimicrobial agent for orthodontic patients. Keywords: colony count, mouthwashes, orthodontic brackets, plant extracts, Streptococcus mutans