N-(4-Hydroxyphenyl) maleimide was synthesized via two synthesizing procedures, and a new bismaleimide bearing polysiloxane (BPS) was prepared by reacting N-(4-hydroxyphenyl) maleimide with dichlorodimethyl silane at first, then the adduct was reacted with polysiloxane terminated by hydroxyl groups. The products were characterized by i.r., n.m.r. and elemental analysis, respectively. The molecular weight of BPS was determined by g.p.c. and its curing behaviour and cured resin thermal stability were investigated by d.s.c. and t.g.a. The toughening effect of BPS was investigated by introducing it into 4,4’-bismaleimido diphenylmethane (BMI) cured matrix. The results indicated that adding 20 wt% BPS into the BMI matrix could increase the impact strength 3.7 times as much as that of the pure BMI matrix. The toughening mechanism of the matrix was elucidated by the glass transition temperature, determined by d.s.c., and the fracture surface morphology was observed by s.e.m.