The present invention relates to a new urethane oligomer (A) and a resin composition comprising (A) and an unsaturated group containing polycarboxylic acid resin (B) that can be diluted with water and is excellent in providing a cured product and that is suitable for a solder resist and an interlayer dielectric layer because the cured product is excellent in flexibility, soldering-heat resistance or the like and allows a development with an organic solvent or a dilute alkali solution; a photosensitive resin composition suitable for an etching resist or a cover lay; and a photosensitive film obtained thereby.