Abstract: The brittleness of epoxy resin needs toughening to meet the application requirements. Protocatechuic acid epoxy resin (PA-EP) was synthesized from protocatechuic acid (PA) and epichlorohydrin via two-step reaction, and used as special epoxy resin for the modification of bisphenol A epoxy resin. The structure and properties of the PA-EP were characterized by fourier transform infrared spectrometer (FTIR), nuclear magnetic resonance spectroscopy (¹HNMR), potentiometric titration and viscosity tester. FTIR, ¹HNMR and viscosity analyses indicate that the target product are synthesized with epoxy value of 0.73 eq/100 g and viscosity of 43.2 Pa·s at 25℃. The mechanical properties of PA-EP/E-51 thermosets are better than others when the mass ratio of PA-EP to E-51 is 10%. The tensile strength, flexural strength and impact strength are increased by 37.4%, 17.2% and 82.9%, respectively. The scanning electron microscope (SEM) images of impact section show that PA-EP/E-51 thermosets exhibit ductile fracture characteristics. Dynamic mechanical analysis (DMA) and thermogravimetry (TG) results indicate that the glass transition temperature (T_g) increases from 116.0℃ (neat E-51) to 137.3℃ with 12.5% of PA-EP/E-51. The weight loss 10% and the maximum decomposition rate temperature are decreased slightly while the residue content of 800℃ increases from 5.9% (neat E-51) to 9.8% (12.5% PA-EP/E-51).