disclosed is a photosensitive diazo resin for lithographic printing represented by the formula : ## str1 ## wherein x - is a counter anion , y is a divalent bonding group selected from the group consisting of -- nh --, -- s -- and -- o --, r 1 , r 2 and r 3 are groups which are independently selected from the group consisting of hydrogen , an alkyl group and an alkoxy group , r 4 and r 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 70 and a is a quaternary ammonium salt - containing group represented by the formula : ## str2 ## . a photosensitive resin composition for lithographic printing comprising a diazo resin is also disclosed .