The hexuronic acid derivative represented by the following formula 1 or a salt thereof is used as an active ingredient of a heparin / heparan sulfate sulfotransferase inhibitor.In the formula, each of R1, R2, and R3 independently represent(s) SO3− or H which may have a substituent, provided that at least one thereof represents SO3−; X represents OR4, SR4, N(R4)2, or C(R4)3, R4 independently represents H, alkyl, alkenyl, alkynyl, acyl, aryl, or aralkyl group; one of R5 and R6 represents COOH while the other represents H; and the wavy line represents α-glycosidic bond or β-glycosidic bond.