Abstract: A protein having an .alpha.-glucosidase activity, wherein its N-terminal amino acid sequence is the sequence depicted in the Sequence Listing of the present invention at Sequence No. 1; a DNA having the genetic information of the protein having an .alpha.-glucosidase activity; a recombinant vector containing said DNA; a transformant transformed with said vector; and production of .alpha.-glucosidase comprising culture of said transformant in a medium so as to grow .alpha.-glucosidase, and harvesting said .alpha.-glucosidase. According to the present invention, .alpha.-glucosidase without contamination of amylase can be easily produced in high yields and in large amounts by genetic engineering.