Abstract: The effect of different reaction temperature and time on product phase is investigated with kaolin and aluminum sulfate as raw materials in molten sodium sulfate.The result indicates the optimum temperature for mullite whisker growth is about 900℃.Alumina generates at 1000℃ and the main phase of specimen all are alumina and sodium aluminum silicate at 1200℃.The mullite whisker is obtained at 900℃ for 2h,with diameter about 0.5μm and length more than 7μm.