Abstract: A light-sensitive composition particularly suitable for making light-sensitive lithographic printing plates is described composed of a mixture of a sensitizer and a photo-crosslinkable polymer, or a mixture of a sensitizer, a compound including a light-sensitive azido group and a polymer reactive with a decomposate of azido groups to be formed upon exposure to light, and a sensitizer represented by the formula (I) ##STR1## wherein A represents a non-metallic atomic group necessary for forming a heterocyclic ring containing nitrogen; R.sub.1 represents an alkyl group or a substituted alkyl group; R.sub.2 represents hydrogen, an alkyl group, a substituted alkyl group, an aryl group, or a substituted aryl group; and Y and Z each represents an oxygen atom or a sulfur atom.

Abstract: A photopolymerizable composition comprising a monomer having at least two ethylenically unsaturated groups, which can be photopolymerized by actinic radiation, a photopolymerization initiator represented by the formula: ##STR1## wherein A represents an arylene group, a substituted arylene group, an alkylene group, a substituted alkylene group, an alkenylene group, or a substituted alkenylene group and R represents an alkyl group, a substituted alkyl group, an aryl group or a substituted aryl group, and optionally a linear organic high molecular weight polymer and a sensitizer. The composition is useful for photosensitive layers of photosensitive printing plates, photoresists, etc.