Uniformly dispersed yttrium aluminum garnet (Y3Al5O12, YAG) ultrafine powders were synthesized by co-precipitating a mixed solution of aluminum and yttrium nitrates with ammonium hydrogen carbonate in the presence of sodium dodecyl sulfate (SIDS) as dispersing agent. The primary purpose of introducing SIDS was to protect YAG particles from agglomeration. The evolution of phase composition and micro-structure of the as-synthesized YAG powders were characterized by thermogravimetry/differential scanning calorimetry. X-ray diffraction, infrared spectra and scanning electron microscopy. The results showed that phase-pure YAG powders could be achieved by calcination of the precursor at 900 degrees C for 2 h. Uniformly dispersed YAG powders with a particle size of approximately 90-100 nm were obtained with optimum molar ratio of Al3+ to SDS at 2. And excessive SDS restrained good dispersion of the YAG powders. The dispersion mechanism of SDS in the preparation process was discussed. (C) 2009 Elsevier B.V. All rights reserved.