Abstract: The CoFe₂O₄/SiO₂ nanocomposite was prepared by the sol-gel method. The structure , crystalline size and magnetic properties of samples were investigated by XRD , TEM , VSM and Mssbauer effect . The results show that the grain size of CoFe₂O₄ increases with the increasing of heating temperature , and the growth of CoFe₂O₄ grain is restricted effectively with the existence of amorphous SiO₂. VSM result s show that the saturation magnetization and coercivity of the samples increase with the increasing of the grain size. With the rise in treatment temperature , the samples transform from the superparamagnetic and magnetic order mixed state to an entire magnetic order state ,which is confirmed by the Mssbauer effect .