Abstract: OBJECTIVE To study the antibacterial activity of grape seed procyanidins (GSPC) against streptococcus mutans in vitro and to explore its anti-caries potential. METHODS Broth micro-dilution method was used to determine minimal inhibitory concentration (MIC)， minimal bactericidal concentration (MBC) and minimal biofilm inhibitory concentration (MBIC); crystal violet semi-quantitative method was used to determine biofilm-formation; anthrone sulfuric acid method was used to test glucan production and pH was used to test acid generation. RESULTS MIC value of GSPC was 12.5 mg/mL while MBC value and MBIC value were both 50 mg/mL. GSPC (≥12.5 mg/mL) could reduce biofilm formation， and especially when its content increased to eight times of MIC content(100 mg/mL)， the inhibition rate was able to achieve 76%. Also it had the ability of inhibiting the glucan production and acid generation at lower content than that of MIC. CONCLUSION GSPC shows antibacterial activity and inhibitory effects on biofilm-formation and cariogenic virulence factors against streptococcus mutans in vitro.