Casting a photopolymer solution to form a film, followed by imagewise photoirradiation and subsequent wet development, leads to photolithography. Whereas the wet development is achievable with aqueous alkali, the emission of an organic solvent as a volatile organic compound (VOC) is usually inevitable during the film casting because ingredients of common photopolymers are insoluble in water. We show here a prototype of water-borne photopolymers dispersed with milled nanoparticles of poorly water-soluble photoacid generators (PAGs), which undergo solidstate photolysis to liberate a photoacid to make a poly(vinyl alcohol) film insoluble in water with the aid of an acid-sensitive crosslinking reagent. The photolysis of onium-type PAGs is sensitized in the solid state simply by comilling with water-insoluble sensitizers to extend spectral sensitivity of this kind of photopolymers. Fluorescence quenching measurements revealed that the solid-state sensitization occurs through exciton migration in sensitizer particles followed by electron transfer to PAG particles.