In the course of our studies on the development of anti-plaque agents for prevent of dental caries, we investigated the effect of some of polyphenolic compounds on the glucosyltransferase from Streptococcus mutans. The structure revealed that the main anti-plaque components of jack fruit extract were (+)-catechin, procyanidin B-3, afzelechin-(4α→8)-catechin and procyanidin C-1. Procyanidin C-1 was the most active component and this compound inhibited on glucosyltransferase noncompetitively.