The thermal stability of the alkaline protease extracellular subtilisin-type serine protease (AprP) from Pseudomonas sp. KFCC 10818 was improved by altering an amino acid residue at an autoproteolytic cleavage site. N-terminal sequence analysis of the autoproteolytic products of the protein revealed the presence of two cleavage sites, Ser-307 and Ser-331. To increase the thermal stability of the enzyme, serine residues of these sites were replaced with aspartate. The S331D mutant enzyme was successfully purified and characterized whereas the S307D mutant was not. The half-lives of the S331D mutant at 55 °C and 60 °C were 1.5 and 2.4 times longer than that of the wild-type enzyme, respectively. In addition, the catalytic efficiency was also enhanced.