A novel sulfotransferase purified from a human intestinal bacterium stoichiometrically catalyzed the transfer of a sulfate group of phenylsulfate esters to phenolic compounds. Vmax values of the enzyme reaction were measured with various concentrations of a sulfate donor substrate, p-nitrophenylsulfate, and of a sulfate acceptor substrate, tyramine. Double reciprocal plots of the acceptor concentration and Vmax showed a linear correlation. One of the reaction products, tyramine O-sulfate, competitively inhibited the enzyme as to a donor substrate, p-nitrophenylsulfate (PNS), but the other reaction product, p-nitrophenol (PNP), noncompetitively inhibited it as to PNS. These kinetic data suggest that the sulfate transfer reaction proceeds according to a ping pong bi bi mechanism. The enzyme was activated by Mg2+ and inhibited by EDTA, which suggests that it is a metalloenzyme.