An efficient method to improve the mechanical performance of a commercially available photocure resin is described wherein the resin is modified with a mixture of a cycloaliphatic epoxy and an anhydride curing agent. Photocured samples are thermally treated in a subsequent step to cure the epoxy to obtain an interpenetrated polymer network (IPN) and also complete reaction of the acrylate monomers remaining from the photocure. The latter is accomplished by a thermal radical initiator added earlier into the formulation together with the epoxy‐anhydride. The thermal properties and microstructure of the resulting IPN are analyzed. Uniform and quantitative conversions are obtained, with glass transition temperatures comparable to conventional epoxies. The liquid, uncured samples containing different amounts of epoxy are stable at 30 °C for several weeks. In the fully cured epoxy‐rich materials, nano‐scale phase separation is observed by atomic force microscopy. This is corroborated by the existence of multiple relaxations determined by dynamic mechanical analysis analysis. Specimens from a formulation containing 50% by weight of epoxy‐anhydride are 3D printed in a customized masked image processing stereolithography, thermally treated, and are subjected to compression tests. Results show that Young's modulus increases by 900% over the neat resin.