Chitinases (glycanohydrolases, EC 3.2.1.14) are important enzymes in various fields such as biological control, pharmaceuticals and chemical purposes as well as food and feed industries. Therefore, the present study aimed to produce chitinase enzyme and the results revealed that: Maximum enzyme activity and cell density of B. stearothermophilus were obtained in the fourth day on the fermentation media containing 1.5% of chitin or chitin + arabinose or/and CM – cellulose as carbon source and 1.5% yeast extract as nitrogen source, which these nutrition factors induced the enzyme biosynthesis. The shaking of culture through the fermentation period greatly enhanced the formation of this enzyme. Initial pH 8.0 and 55°C as incubation temperature were found as the best environmental factors for enzyme production. 65% is the best saturation of ammonium sulphate which gives higher enzyme activity, recovery and purification folds. The purification of enzyme with DEAE – sephadex A – 50 gives higher purification folds and specific activity of enzyme. The fractionation of enzyme preparation showed 3 peaks of enzyme. This means that, this enzyme has three fractions of chitinase, which identified as three types of endo – chitinase. pH 6.0 and 65°C were found as the optima for enzyme activity. The enzyme showed higher stability against the different pH range between 5.0 to 8.0 and completely stable at pH 6.0. This means that the enzyme protein has acidic in its nature. Also, the enzyme was stable up to 75°C and lost little activity from its maximum up to 85°C.  This means that, this enzyme was a thermostable one. Some metal ions activated the enzyme activity such as Mg⁺² and Ca⁺², but others such as Ag⁺ and Hg⁺² were inhibited it. Enzyme preparations were successfully to hydrolysis different substrates with higher degree such as colloidal chitin, chitin and colloidal chitosan, but other such as dioligomer did not hydrolyze. This is may be due to its substrate specificity or substrate affinity of the enzyme. The enzyme also successfully to hydrolyse cell walls of some plant pathogenic fungi with higher degree. Also prevent the growth of these plant pathogenic as well as sporulation rate. This means that, this enzyme preparation may be used as a good antifungal agent in biological control or preventing the mould growth of pathogenic fungi.