To ascertain the effect of chitin-binding domain (ChBD) and fibronectin type III domain (FN3) on the characterization of the intact chitinase from Bacillus thuringiensis. An intact chitinase gene (chi74) from B. thuringiensis HZP7 and its truncated genes (chi54, chi63 and chi66) were expressed in Escherichia coli BL21. The expression products were analyzed after purification. All chitinases were active from pH 4-7.5 and from 20 to 80 A degrees C with identical optimal: pH 5.5 and 60 A degrees C. The activity of colloid chitin degradation for Chi74 was the highest, followed by Chi66, Chi63 and Chi54. Ag+ reduced the activity of Chi74, Chi54, Chi63 and Chi66, but Mg2+ enhanced them. The effect of Ag+ and Mg2+ was more significant on the activity of Chi54 than on the activities of Chi63, Chi66 and Chi74. ChBD(Chi74) and FN3(Chi74) domains play a role in exerting enzymatic activity and can improve the stability of chitinase.