The ability to produce extracellular chitosanase (EC 188.8.131.52) was found by plate assays in 18 (23 %) out of 77 crystalliferous strains ofBacillus thuringiensis. The best chitosanase producer was selected after the growth chosen in a liquid medium with colloidal chitosan as carbon source. Enzyme production was optimized (a 4-d incubation at 32 °C with shaking in a medium of pH 6.5 with 4 % colloidal chitosan) and the enzyme was partially characterized. This is the first report on the chitosanase ofB. thuringiensis.