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 R.sub.1, R.sub.2, and R.sub.3 independently represent(s) SO.sub.3.sup.- or H which may have a substituent, provided that at least one thereof represents SO.sub.3.sup.-; X represents OR.sub.4, SR.sub.4, N(R.sub.4).sub.2, or C(R.sub.4).sub.3, R.sub.4 independently represents H, alkyl, alkenyl, alkynyl, acyl, aryl, or aralkyl group; one of R.sub.5 and R.sub.6 represents COOH while the other represents H; and the wavy line represents .alpha.-glycosidic bond or .beta.-glycosidic bond.