An extracellular cellulase from Thalassobacillus sp. LY18 was purified 4.5-fold with a recovery of 21 % and a specific activity of 52.4 U mg(-1) protein. Its molecular mass was 61 kDa estimated by SDS-PAGE. It was an endoglucanase for soluble cellulose with optimal activity was at 60 A degrees C and pH 8 with 10 % (w/v) NaCl. It was stable from 30 to 80 A degrees C and from pH 7 to 11 with NaCl from 5 to 17.5 % (w/v). EDTA inhibited activity indicating it was a metalloenzyme. Inhibition by diethyl pyrocarbonate and beta-mercaptoethanol suggested that histidine residues and disulfide bonds may play important roles in its catalytic function. The cellulase was highly active in non-ionic surfactants and was stable in water-insoluble organic solvents with log P (ow) a parts per thousand yen 2.13.