This paper deals with the applications of Response Surface Methodology (RSM) on the effect of microwave heat treatment for mullite formation from placer sillimanite. The results of these investigations reveal that RSM data obtained from microwave heat treatment studies show that there is 92.55% of mullite formation under optimized conditions with composite charge material having 40% Al2O3, 60% sillimanite, with additive 60% SiC and 10% binder. The confirmatory experimental data of RSM optimised conditions also suggest that there is 97% of mullite formation using microwave heat treatment. A mullite is formed within 25 minutes from the sillimanite, under the above experimental conditions. FESEM image analysis shows the mullite formations in cluster form, SiC in massive structure and alumina needle form in microwave treated sample. Thus microwave heat source is much effective to form mullite from sillimanite.