Tea and fruit juices are beverages consumed daily all over the world. The present study reports the inhibitory effects of these beverages on the activity of mammalian intestinal phenol sulfotransferases (P-STs).Green tea strongly inhibited the E. coli-expressed mouse intestinal P-ST activity in vitro. (-)-Epigallocatechin gallate (EGCG) was found to be the most potent inhibitor among the catechins tested (IC₅₀=0.93 μM). (-)EGCG also inhibited the P-ST activity of the human colon carcinoma cell line, Caco-2. Kinetic analysis showed that the inhibition was competitive. Among fruit juices examined (apple, grape, grapefruit and orange), grape juice exhibited the most potent inhibitory action on the P-ST activity of mouse intestines and human colon carcinoma cells. The inhibitory activity of grape juice was located mainly in the skin and seels. Flavonols, such as quercetin and kaempferol, inhibited the P-ST activity at low concentrations. These observations suggest the possible inhibition of P-St activity in human intestines by green tea or grape juice.