AbstractBacillus sp. MG-33 was isolated from the desert of Rajasthan (India). The organism produced 500 and 200 Ug-1 of thermostable mannanase (after 96h) in solid state fermentation (SSF) of wheat bran and wheat straw rich-soda pulp at the moisture ratio of 1:1.5 and 1:3 at 30ºC, respectively. Two-step partially purified mannanase was optimally active at 65ºC and was 100% thermostable at 55 to 60ºC for 2h and also retained more than 50% residual activity at 65ºC for 2h. A pH of 6.5 was optimum for enzyme activity and 100% stability up to 4h at this pH. Mannanase activity was slightly enhanced by Ca2+, Fe3+, and Mg2+, while 100% activity was retained in the presence of Ba3+, Li+, and NiCl2 at 1.0-10mM. 1M NaCl and urea did not reduce the enzyme activity. The Km and Vmax of mannanase were 0.2mgml-1 and 60Umg-1ml-1, respectively. Hydrolysis of locust bean was rapid and linear between 5 and 20 min, and ~300µgml-1 mannose was obtained after 20 min of catalytic reaction by enzyme at 65ºC. TLC was used to confirm the mannose as an end product after hydrolysis of locust bean gum.