Cultural conditions for $alpha$-D-Glucosidase Inhibitor production from Streptomyces sp. YS-221-B isolated from soil arid identified as Streptomyces flauovirens or a subspecies of it were investigated. When the strain was cultured in a flask containing 2% glucose, 0.3% asparagine, 0.0002% riboflavin, 0.05% $K_2$HPO$_4$, 0.1% MgSO$_4$.7$H_2O$, 0.05% NaCl, pH 8.0 at 3$0^{circ}C$, maximum production of the inhibitor was obtained after 8-9 days of cultivation. Sugar alcohols such as mannitol, i-inositol, erythritol as carbon sources, asparagine and beef extract as nitrogen sources were favorable for inhibitor production. Among vitamins, riboflavin, p-aminobenzoic acid, pyridoxamine and folic acid promoted the production of inhibitor, but depressed by the addition of hesperidine, and also depressed by cobalt, lithium and ferrous salts.