A solvent-free resin composition comprising (a) a polyimide silicone resin having repeating units represented by the following general formulas (1-1) and (1-2), ##STR00001## wherein X is a tetravalent organic group, Y is a divalent organic group, and Z is a divalent organic group having an organosiloxane moiety, (b) a reactive diluent, and (c) a photo-polymerization initiator, characterized in that a film of said resin composition with a film thickness of 100 .mu.m prepared on a quartz glass substrate shows a light transmittance of 80% or higher at wavelengths of from 350 nm to 450 nm.