Disclosed is an efficient method for production of aminopeptidase. The method comprises either transforming host bacteria with an aminopeptidase gene and with a neutral protease gene, or transforming some part of host bacteria with an aminopeptidase gene while transforming the other part of the host bacteria with a neutral protease gene, culturing in a medium the hose bacteria transformed with the aminopeptidase gene and with the neutral protease gene, or culturing a mixture of the host bacteria transformed with the aminopeptidase gene and the host bacteria transformed with the neutral protease gene, to let both the aminopeptidase and the neutral protease be expressed, and collecting the aminopeptidase thus produced from the culture mixture.