A novel type of arylsulfotransferase was partially purified from human intestinal bacteria and its enzymatic properties were examined. Polyphenols such as chalcone, xanthone and flavonoid were found to be sulfated by the bacterial arylsulfotransferase though the sulfation activity varied depending upon the positions of the hydroxyl groups. Quercetin, as an example of a flavonol, was rapidly sulfated when p-nitrophenyl sulfate (PNS) was taken as a donor substrate. At a ten-fold molar excess of PNS over quercetin, two products, the 3,3'-disulfate and 3,3',7-trisulfate derivatives, were formed, but the 4'- and 5-hydroxyl groups were not sulfated. In the case of equimolar or two-fold molar excess of PNS to quercetin, only the 3,3'-disulfate was produced and no monosulfate was formed. The enzymatic procedure is useful as a specific and convenient method for the preparation of polyphenol sulfate esters.