This study reports the purification and biochemical characterization of a novel maltotetraose-forming-${alpha}$-amylase from Pseudomonas stutzeri AS22, designated PSA. The P. stutzeri ${alpha}$-amylase (PSA) was purified from the culture supernatant to homogeneity by Sepharose mono Q anion exchange chromatography, ultrafiltration and Sephadex G-100 gel filtration, with a 37.32-fold increase in specific activity, and 31% recovery. PSA showed a molecular weight of approximately 57 kDa by SDS-PAGE. The N-terminal amino acid sequence of the first 7 amino acids was DQAGKSP. This enzyme exhibited maximum activity at pH 8.0 and $55^{circ}C$, performed stably over a broad range of pH 5.0 ~ 12.0, but rapidly lost activity above $50^{circ}C$. Both potato starch and $Ca^{2+}$ ions have a protective effect on the thermal stability of PSA. The enzyme activity was inhibited by $Hg^{2+}$, $Mn^{2+}$, $Cd^{2+}$, $Cu^{2+}$, and $Co^{2+}$, and enhanced by $Ba^{2+}$. PSA belonged to the EDTA-sensitive ${alpha}$-amylase. The purified enzyme showed high stability towards surfactants (Tween 20, Tween 80 and Triton X-100), and oxidizing agents, such as sodium per borate and $H_2O_2$. In addition, PSA showed excellent compatibility with a wide range of commercial solid and liquid detergents at $30^{circ}C$, suggesting potential application in the detergent industry. Maltotetraose was the specific end product obtained after hydrolysis of starch by the enzyme for an extended period of time, and was not further degraded.