The control of the rhodium particle size of silica-supported catalysts by using microemulsion was investigated in terms of the structure of surfactants and organic solvents. The use of nonionic surfactants and anionic surfactants is effective for the preparation of catalysts having narrow size distribution. Especially, in nonionic surfactants, the rhodium particle size varied in the range of 3.0-8.2 nm according to the structure of surfactants and organic solvents regardless of rhodium content. The length of the hydrophilic group of surfactants and the carbon number of n-alcohol as an organic solvent were effective factors for the size control. The rhodium particle size increased with decreasing length of the hydrophilic groups of surfactants and with increasing carbon number of n-alcohol.