The glassy composite materials were prepared by quenching the phase separated melts in two-liquids immiscibility region of Fe3O 4-TiO2-SiO2 ternary system. The fine phase-separation textures which consisted of Fe-Ti rich phase and Si rich one were formed in the samples, and the precipitation of Fe3O 4-TiO2 solid solution was observed in the samples of the specific compositions. The samples containing Fe3O 4-TiO2 solid solution showed ferrimagnetic properties on their magnetization curves. In low Fe3O4-TiO2 content, coercivity increased with increase of Fe3O 4-TiO2 content since the precipitated particles in the samples grew and had single magnetic domain. In high Fe3O 4-TiO2 content, the coercivity decreased with increase of Fe3O4-TiO2 content because the magnetostatical interparticle interaction among the precipitated particles appeared. These results indicate that the magnetic properties of the composite materials owing to the crystalline phase and its size can be controlled by utilizing the phase separation in this system.