A series of acrylic copolymer modifiers with mesogenic side chain (LCGMB) were synthesized and used to modify E-51/DDM system. The dynamic mechanical behavior and impact strength of the modified systems were investigated. The results showed that the impact strength and modulus were influenced by the composition and the amounts of the modifiers. With addition of 10% (wt %) LCGMB (molar ratio of GMA : HEMA.: MMA : BA = 4 : 10 : 26 : 60) based on the amount of the epoxy resin, the modified systems obtained 100% increase in impact strength, 10% increase in modulus, and a little increase in Tg. The toughening mechanism of the modified systems was also discussed.