Molecular weight of Exo-maltotetraohydrolase produced by Pseudomonas stutzeri IAM 12097 was estimated to be approrimately 63,000 and 60,000 with SDS-polyacrylamide gel electrophoresis and Sephadex-G-100 gel filtration, respectively. The isoelectric point was appeared to be pH 4.8. Optimum pH, the stable pH range and optimum temperature of this enzyme were pH 6.6, pH 6.0∼10.5 and 45∼50℃. The enzyme was stable below 40℃ and was rapidly inactivated above 55℃. This enzyme was inactivated completely by Ag^+, Hg^(++), I₂ and β-cycoldextrin, and slightly by EDTA, ρ-CMB and IAA. Michaelis constant(Km) of this enzyme toward soluble starch, amylose and amylopectin were 7.70㎎/㎖, 6.17㎎/㎖, 5.56㎎/㎖, respectively.