Abstract: Ni_0.5Co_0.5Fe₂O₄ ferrite nanopowders prepared by the hydro-thermal method were used to toughen cyanate ester-epoxy resin (CE-EP). The effect of Ni_0.5Co_0.5Fe₂O₄ ferrite on the curing reaction, mechanical properties and thermal stability of the CE-EP resins was studied. The XRD and SEM results indicate that the synthesized Ni_0.5Co_0.5Fe₂O₄ ferrite has good crystallinity, purity and block shape, and its particle size is about 20 nm. The performance study shows that the addition of Ni_0.5Co_0.5Fe₂O₄ ferrite has little effect on the curing reaction speed between CE and EP, and does not change the curing mechanism of the resin matrix. Compared with the pure resin system, the Ni_0.5Co_0.5Fe₂O₄ ferrite/CE-EP composites obviously improve their toughness on the basis of maintaining the glass transition temperature (T_g) of the CE-EP resins. When the Ni_0.5Co_0.5Fe₂O₄ ferrite content is 3wt%, the impact strength and the bending strength of Ni_0.5Co_0.5Fe₂O₄ ferrite/CE-EP composites reach the maximum, which are increased by 65% and 30.3% compared with the pure resin matrix, respectively. However, the thermal decomposition temperature of the Ni_0.5Co_0.5Fe₂O₄ ferrite/CE-EP composites decreases slightly, which may be due to the catalytic effect of the Ni_0.5Co_0.5Fe₂O₄ ferrite on the decomposition of the resin matrix.