The spherical mullite fine powder was fabricated by sol-gel method in order to let it have highly functional property. By using ASB[Aluminium tri-sec butoxide] and TEOS[Tetraethyl orthosilicate] as precursors, n-octanol as asolvents and acetonitrile as a solvent for phase seperation by emulsion and HPC[Hyroxypropyl cellulose]as dispersant, well dispersed spherical mullite powder was synthesized. From the result of TG-DTA analysis of dried gel, an exothermic peak was ppeared at about 980 ℃ and it was thought that the procedure of crystallization would arise at over this temperature. Also from the results of XRD of calcined powder, the peak of A1-Si spinel was appeared at the sample which is calcined at 1000 ℃ for 10 hours and the peak of mullite was appeared at 1300, 1400 ℃ for 3 hours. the former sample had an average particle size of 0.316 μm but the latter samples had 0.277 and 0.267 μm respectively in the form os sphere. This significant reduction of particle size resulted from structural transition of A1-Si spinel to mullite phase.