Yb：YAG nanopowders were synthesized by the alcohol-water co-precipitatlon method adding MgO as sintering additives. Appropriate amount of MgO adding can restrict the agglomeration and reduce the particle size of Yb：YAG powders. When the MgO content was 0.04wt%, well-dispersed Yb：YAG powders with ellipsoidal particles of less than 100 nm diameter were obtained. The experimental results showed the valence variation of doping ion Yb〉 would not appear when adding MgO as sintering additives, so ceramics showed colorless transparent instead of green due to Yb^2＋ color center using traditional SiO2 as additives. The transmission of the sintered Yb：YAG ceramics can reach 80.6% even without annealing. Ceramic morphology showed that the grains had uniform-distribution with the size of 10 iam or so, and no impurity and pore existed in the grain boundary and crystalline while using optimal sintering conditions.
