Abstract A marine bacterium Bacillus firmus CAS 7 produced protease in the medium supplemented with 3:1 shrimp and crab shell powder at 55°C and purified with the specific activity of 473.4U/mg. The purified protease was highly stable up to 70°C, pH 11.0 and 30% NaCl. The protease purified was quite stable in the presence of anionic and non-ionic surfactants and organic solvents. The molecular dynamics simulation confirmed that the competition between organic solvent and water for the enzyme surface was comparatively higher in water–miscible organic solvent which is responsible for organic solvent stability. The purified protease from B. firmus CAS 7 could be greatly useful to develop industrial processes performed under harsh conditions or with denaturants and organic solvents. The protease production by microbial conversion of marine wastes suggested its potential utilization to generate high value-added products.