Disclosed herein are the derivatives of substituted cephalosporanic acid represented by the formula (I): ##STR1## wherein R.sup.1 represents a 4-pyridylthiomethyl group, an alpha-aminobenzyl group, a cyanomethyl group or a 1-tetrazolylmethyl group; R.sup.2 represents a hydrogen atom, an acetoxy group or a (5-methyl-1,3,4-thiadiazol-2-yl)thio group; R.sup.3 represents a hydrogen atom, a hydroxyl group, a carbamoyl group, an alkyl group having 1 to 4 carbon atoms or --(CONH).sub.m (CH.sub.2).sub.n --COOH wherein m is 0 or 1, n is 0, 1 or 2 and the carboxyl group may have been converted to a salt or an ester thereof; p is 0, 1 or 2 and X represents carbon atom or nitrogen atom, and antibiotics comprising the derivatives of substituted cephalosporanic acid represented by the formula (I).