Disclosed are a light sensitive composition comprising an addition polymerizable ethylenically unsaturated monomer, a photopolymerization initiator and a polymer binder, and a light sensitive planographic printing plate material comprising a hydrophilic support, and provided thereon, the light sensitive composition, wherein the photopolymerization initiator is a trihalomethyl group-containing oxadiazole compound represented by the following formula 1 or 2, ##STR1##