In this paper, the phase transition of titanium slag under microwave heating observed through electron microscopy was systematically investigated. The phase identification and transformation as well as the morphology of samples before and after each treatment were characterized using X-ray powder diffraction (XRD), Fouriertransform infrared spectroscopy, Raman spectroscopy and scanning electron microscopy (SEM). The XRD confirmed that sodium salt roasting could modify the phase composition of titanium slag. The microwave roasting in the presence of sodium salt increased the rutile TiO2 with high crystallinity after acid leaching. The Raman spectroscopy demonstrated the phase transition of titanium slag from anosovite to rutile TiO2 after a series of treatments, and the SEM analyses showed that the surface of calcined products grew plenty of rutile TiO2 with typical characteristics. The results indicate a successful process for an effective and efficient way for the utilization of both titanium slag and preparation of retile TiO2.