Y3Al5O12 (YAG) nanopowders were synthesized by co-precipitation method with ammonium hydrogen carbonate (AHC) used as precipitator, while ammonium sulfate (AS) was adopted as steric stabilizer and electrostatic stabilizer. The crystallized pure phase of YAG is well obtained when calcined at 1000 C for 2 h. The influence of (NH4)(2)SO4 as the dispersing agent in the reaction system was systematically investigated. Appropriate stoichiometric amount of sulfate has a positive effect on the average particle sizes and the powders agglomerate state. When the molar ratio of AS to nitrate is 0.625, the powder has the best dispersive properties with the smallest mean particle size of about 40 nm. Moreover, the DLVO theory is used to illuminate the underlying physical mechanism. (C) 2011 Elsevier B.V. All rights reserved.