An enzyme which acts on a reducing terminal of a monosaccharide or oligosaccharide without requiring NAD or NADP and which catalyzes the reaction ##STR1## wherein R is a saccharide chain residue or hydrogen, A is a hydrogen acceptor other than NAD or NADP, AH or AHn is a reduced form acceptor and n is 1 or 2. This maltose dehydrogenase is produced by culturing a microorganism belonging to genus Staphylococcus, specifically, sp. B-0875 FERM BP-385, and isolating the thus-produced maltose dehydrogenase from the culture medium. An assay method for the determination of saccharide or the activity of a saccharide liberating enzyme, comprises reacting this enzyme with a substrate in the presence of a hydrogen acceptor, and measuring the amount of a detectable change.