Aims: An investigation was carried out on the enhancement of protease production and simple purification of an oxidant and SDS-stable alkaline protease produced by Bacillus clausii I-52 of industrial significance. Methods and Results: The supplementation with 0.4% (w/v) NaCl and 0.05% (w/v) FeSO4.7H(2)O in a culture medium caused an increase in the protease production. The enzyme was purified to homogeneity with overall recovery of 79% and 10-fold purification from culture supernatant using Diaion HPA75, phenyl-Sepharose and DEAE-Sepharose column chromatographies. The protease was a halo-tolerant enzyme with apparent molecular mass of 28 kDa, and the K-m and k(cat) values for N-Succinyl-Ala-Ala-Pro-Phe-pNA at 45degreesC and pH 11.0 were determined to be 83.9 mumol l(-1) and 238.6 s(-1) respectively. Conclusions: Bacillus clausii I-52 was identified as a halo-tolerant bacterium, and the extracellular alkaline protease produced by B. clausii I-52 also showed extreme halo-tolerance. The enzyme stability towards SDS and H2O2 could be increased by adding NaCl or propylene glycol to the enzyme solution. Significance and Impact of the Study: The alkaline protease secreted by B. clausii I-52 is significant from an industrial perspective because of its stability against surfactants and oxidants as well as its tolerance towards high salinity. These enzymatic properties suggest its suitable application for industrial purposes.