<p>1-Deoxymannojirimycin represented by the general formula [I] which is a potent inhibitor against alpha -mannosidase and affects the biosynthesis of glycoprotein and inhibits sugar chain processing and is thus expected to be an immune regulator, can be manufactured by a method which comprises culturing a microorganism belonging to the genus Streptomyces and capable of producing 1-deoxymannojirimycin in a medium, and isolating 1-deoxymannojirimycin from the culture broth. <CHEM> x</p>
