Providing an alkaline protease exhibiting an improved solubility in a liquid detergent. A mutant alkaline protease consisting of the amino acid sequence represented by SEQ ID No: 2 or an amino acid sequence having 80% or more sequence identity therewith, in which at least one amino acid residue selected from the group consisting of the amino acid residues at predetermined positions of the amino acid sequence represented by SEQ ID No: 2 or corresponding positions thereto are substituted.
