Abstract: Taking silica fume and aluminum sulfate as raw materials, sodium sulfate as reaction medium, mullite whiskers were prepared by reaction sintering technology. The effects of sintering temperature and time on the phase of products were studied. The results show that the optimum sintering temperature and time of mullite whisker growth were 900 ℃ and 1-2 h, respectively. Alumina and sodium aluminium silicate generated when sintering time was 3 h or sintering temperature was over 900 ℃. The mullite whiskers with diameter of 0.03-0.6 μm and with maximum length over 6 μm was obtained after sintering at 900 ℃ for 2 h.