A thermal negative type lithographic printing original plate has a photosensitive layer featuring high sensitivity, excellent reproducibility in FM screening, and excellent print durability and chemical resistance at a minute image portion. A photosensitive composition for the photosensitive layer contains an alkali soluble resin having a monomer unit represented by the formula (I), a silane coupling agent represented by the formula (II), an infrared absorber, a radical polymerization initiator, and a polymerizable compound having an ethylenic double bond and an amount of the silane coupling agent is from 15 to 40% of the photosensitive composition by mass.