Disclosed is a photosensitive diazo resin for lithographic printing represented by the formula: ##STR1## wherein X.sup.- is a counter anion, Y is a divalent bonding group selected from the group consisting of --NH--, --S-- and --O--, R.sub.1, R.sub.2 and R.sub.3 are groups which are independently selected from the group consisting of hydrogen, an alkyl group and an alkoxy group, R.sub.4 and R.sub.5 are groups which are independently selected from the group consisting of hydrogen, an alkyl group and a phenyl group, 1 and m are integers which satisfy the relation:1+m=2 to 100, 1/m=30 to 99/1 to 70and A is a quaternary ammonium salt-containing group represented by the formula: ##STR2## (wherein B is a straight or branched divalent C.sub.1-10 alkyl group which bonds to an aromatic ring by a group selected from the group consisting of --CH.sub.2 --, --CO--, --O--, --S-- and --N--, and R.sub.6, R.sub.7 and R.sub.8 are groups which are independently selected from the group consisting of hydrogen and a C.sub.1-20 alkyl group provided that at least two of R.sub.6, R.sub.7 and R.sub.8 are alkyl groups). A photosensitive resin composition for lithographic printing comprising a diazo resin is also disclosed.