Mullite whiskers were synthesized using $Al(OH)_3$, amorphous $SiO_2$ and $AIF_3$ as starting materials by a vapor-solid reaction at relatively low temperature of $1100^{circ}C$. Leaflet Fluorotopaz was observed for the specimen heat-treated at $800^{circ}C$. Fluorotopaz was decomposed at $1000^{circ}C$ and only mullite phase was observed for the specimen sintered at $1100^{circ}C$ and above. It was found that the synthesized mullite at $1200^{circ}C$ had grown to [001] direction and side planes were the {110}. The distance of (110} plane was $5.34^{AA}C$. The amounts of $Al_2O_3$ in mullite was 73.56(1.39)wt%.