The effects of poly (methyl methacrylate-b-butyl acrylate-b-methyl methacrylate) (PMBM) on the impact strength and other properties of poly (methyl methacrylate) (PMMA) were investigated in this work. Low addition level of PMBM with composition of 6kPMMA-53kPBA-6kPMMA has remarkable improvement on the impact resistance of PMMA. The highest impact strength of 4.76 kJ/m2 with increase of 126% relative that of PMMA is achieved by addition of 3% PMBM. The mass fraction of PMMA segment in PMBM also exhibits great effect on the impact resistance of PMMA when the mass fraction of PBA is kept constant. The highest impact strength increase of 86% relative to that of PMMA is achieved when the mass fraction of PMMA segment is 42.5%. Scanning electron microscope analysis reveals that the impact fracture surface of PMBM/PMMA blends exhibits ductile fracture characteristic. The heat resistant and transmittance properties are changed little by addition of PMBM as revealed by dynamic thermomechanical analysis and transmittance spectrometer.