Introduction: The Persian toothbrush tree or Miswak (Salvadora Persica L.) has been used as a brushing stick for more than 1,300 years. Pharmacological studies indicated antibacterial and antiinflammatory activities of Miswak extract. The present study was performed to determine antibacterial effects of Miswak extract.Material and Methods: The present experimental research involved three in vitro studies including: 1) in vitro testing of the effect of Miswak extract on selected bacteria; 2) comparing the paraclinical effects of Iranian toothpaste containing Miswak extract and placebo toothpaste on dental plaque; and 3) comparing the antibacterial effect of Iranian toothpaste with Swiss toothpaste(Quail Miswak) on dental plaque. The disc diffusion method was used to test bacterial sensitivity of toothpastes. Data were analyzed by paired t-test and ANOVA.Results: In the first study, Miswak extract inhibited the growth of some dental plaque bacteria. In the second study, antibacterial effect of the herbal toothpaste was significantly greater than that of the placebo (P =0.002). In the third study, four samples of dental plaque bacteria were used and there was no difference between the antibacterial effects of Swiss and Iranian herbal toothpastes (P =0.66).Conclusion: Due to antimicrobial effects of Miswak extract, its use in mouth rinses and toothpastes is highly recommended.