A Bacillus sp. US100 strain was isolated from Trunisian hot spring soil. This strain secretes a thermoactive amylase having an optimal temperature of 82 degrees C and a remarkable thermostability with a half time of 40 min at 110 degrees C in the presence of 20% (w/v) of substrate. The main end products of its action an starch are maltohexaose and maltopentaose which is the smallest substrate hydrolyzed by this enzyme. The molecular cloning, in E. coli, of a 3-kb DNA fragment encoding far this activity is also reported