protease production by thermophilic bacillus sp strain smia-2 cultivated in liquid cultures containing trisodium citrate reached a maximum in 9h, with levels of 1.93u/mg protein. the microorganism utilized several carbon sources for the production of protease. starch was the best substrate, followed by trisodium citrate, citric acid and sucrose. among the various organic and inorganic nitrogen sources, ammonium nitrate was found to be the best. studies on the protease characterization revealed that the optimum temperature of this enzyme was 60oc. the enzyme was stable for 2h at 30oc, while at 40oc and 80oc, 14% and 84% of the original activities were lost, respectively. the optimum ph of the enzyme was found to be 8.0. after incubation of crude enzyme solution for 24h at ph 5.5, 8.0 and 9.0, a decrease of about 51%, 18% and 66% of its original activity was observed respectively. a stronger inhibitory effect was observed in the presence of k+, hg2+and cu2+. hg+ resulted in the complete loss of activity at 1mm concentrations. activity was stimulated by mn2+ and ca+2, indicating that these ions had a functional role in the molecular structure of the enzyme.