We present a novel antisolvent processing technique by simultaneous compressed antisolvent precipitation and photopolymerization for forming cross-linked polymer microparticles. In this process, an organic solvent dissolves monomer and polymerization photoinitiators to form a homogeneous solution. Photopolymerization and microparticle formation occur when the homogeneous solution is sprayed into a compressed antisolvent while being simultaneously exposed to initiating light. High miscibility of the solvent in the supercritical antisolvent allows for its quick extraction from the polymerizing phase, leaving progressively higher concentrations of monomer. The high monomer concentration combined with photoinitiated polymerization facilitates rapid reaction rates and ultimately results in polymer precipitation. Particle size and morphology are adjustable by changing the processing conditions, as simultaneous polymerization and solvent extraction result in microparticles with a wide range of diameters.