Neutral cellulase was purified from a culture of mixed thermophilic bacilli. After purification, its mol weight was found to be 42 KDa, composed of two subunits of 22 KDa and 20 KDa, by SDS-PAGE. The activity of this neutral cellulase was optimum at pH 7 and 60℃ and stable at a pH range of 5 to 10 and up to 65℃. The cellulase could hydrolyze some insoluble celluloses although the activity was not so powerful.