Epoxy monoacrylate resins are widely used in a myriad of industrial applications; however, their shelf life still requires improvement. This work investigates the use of acryl phosphate [mixture of 2- (methacryloyloxy)ethyl phosphate and bis(2-(methacryloyloxy)ethyl) phosphate] as a reactive additive to increase the long-term storage stability of epoxy monoacrylate resins. A series of epoxy monoacrylate resins were synthesized via addition esterification reaction of diglycidylether bisphenol-A (DGEBA) with acrylic acid at different mole ratios. The epoxy equivalent weight, viscosity, and acrylation portion of the synthesized epoxy monoacrylate resin increased with increasing the acrylic acid content, and the optimization of the mole ratio of DGEBA and acrylic acid allowed obtaining a high-purity epoxy monoacrylate resin. The investigation of the storage stability of the epoxy monoacrylate resin formulated with acryl phosphate revealed that no viscosity was developed after 12 weeks, which demonstrates that the additive increased the long-term shelf life of the resin.