TiO2/(O + β)-Sialon multiphase ceramics were prepared with nano Ti O2 (anatase) powder and (O + β)-Sialon powder as raw materials. Effect of Yb2O3 additive on transformation behavior of anatase for TiO2/(O + β)-Sialon multi phase ceramic was investigated and its influence mechanism was discussed. XRD was employed for the analysis of phase composition and lattice parameters. The results show that even though Yb2O3 has no obvious influence on starting temperature of phase transformation, it significantly accelerates the transformation process, which displays a weakened effect with more Yb2O3 addition. There exist two forms of the added Yb2O3: some enters TiO2 lattice and the other deposits on the surface of TiO2. The function of Yb2O3 on phase transformation of anatase can be attributed to the coaction of active and negative influence mechanisms as follows: some Ybn+ enter TiO2 lattice and replace Ti4+ , as well as the redox reaction between Yb3 + and TiO2, which promote the transformation, whereas other Yb2O3 deposits on the surface of TiO2, and TiO-Yb bond is formed by the coaction of Yb3 + and TiO2, which inhibit the process.