The Ni0.5Zn0.5Fe2O4/SiO2 composite nanofibers were prepared using sol-gel process combined with electrospinning. The thermal decomposition and phase inversion process of precursor nanofibers and the effects of calcination temperature and SiO2 content on the phase composition, microstructure, morphology and magnetic property of the resulting nanofibers were studied by means of thermogravimetric and differential thermal analysis, X-ray diffraction, field emission scanning electron microscopy, high resolution transmission electron microscopy and vibrating sample magnetometer. The experimental results show that the cubic spinel structure is basically formed when the precursor nanofibers are calcined at 450 ℃ for 2 h. The average grain size of Ni0.5Zn0.5Fe2O4 contained in the composite nanofibers with 10 % SiO2 and their specific saturation magnetization and coercivity increase with increasing calcination temperature. Amorphous SiO2 additive can effectively restrain the growth of Ni0.5Zn0.5Fe2O4 nanocrystals. As a result, with SiO2 content increasing from 0 to 20 % , the average grain size of Ni0.5Zn0.5Fe2O4 in the prepared Ni0.5Zn0.5Fe2O4/SiO2 composite nanofibers calcined at 900 ℃ for 2 h decreases from 81.6 to 13.3 nm, and the specific saturation magnetization of these samples monotonically decreases, whereas the coercivity initially increases and then decreases due to the change of magnetic domain structure from multi-domain to single-domain along with the reduction in grain size. In addition, with the increase of SiO2 content, the diameter of the as-prepared Ni0.5Zn0.5Fe2O4/SiO2 composite nanofibers gradually increases and the surface becomes smooth.