Starting from a commercial preparation of Bacillus thuringiensis var. aizawai, widely employed as biopesticide in agriculture, we obtained a chitosanolytic activity by washing the cells with concentrated sodium acetate. The optimum pH and temperature values for this enzyme were 6.0 and 60 degrees C, respectively. The enzymatic extract efficiently hydrolyzed various chitosans with different deacetylation degrees (DD) into small oligosaccharides. Combining mass spectrometry (ESI-Q-TOF) and high-performance anion-exchange chromatography with pulsed amperometric detection (HPAEC-PAD), we observed the formation of fully deacetylated chitooligosaccharides [fdCOS, (GlcN)(2.5)] and, to a lesser extent, partially acetylated chitooligosaccharides [paCOS, GIcNAc-(GlcN)(1-3)]. A 10 g/L solution of chitosan with 600-800 kDa and DD >= 90% was fully converted into oligosaccharides in 55 h. Most of the products were fdCOS: 1.6 g/L of chitobiose, 1.7 g/L of chitotriose, 5 g/L of chitotetraose and 1.4 g/L of chitopentaose.