A treated substrate having a hydrophilic region and a water repellent region, of which contrast is high on its surface; a process for producing a treated substrate, wherein the treated substrate can be produced with a low amount of light for a short time; wherein the water repellent region is made of a water repellent film formed by curing the composition (A) comprising a photopolymerization initiator and a compound (a) having at least one (meth)acryloyl group, and a water repellent moiety and having a film thickness of from 0.1 to 100 nm; the process uses a hydrophilic substrate or makes the surface thereof hydrophilic, then forms a film containing the composition (A) on the surface, then forms said water repellent film by irradiating light on a part of the film surface to cure the composition (A) and then removes an uncured composition (A) present thereon in order to expose the hydrophilic surface.