Objective： The gene cloning and expression of glutamate decarboxylase A from Escherichia coli and its enzymatic properties were investigated. Methods： The gene gadA encoding glutamate decarboxylase A from E. coli was amplified by PCR， and was cloned into the vector pET-28a（+） to construct recombinant plasmid pET28a- gadA， which was then transformed into E. coli BL21 to generate the strain E. coli BL21/pET28a-gadA. Glutamate decarboxylase A was purified by Ni2+ affinity chromatographic column， and its enzymatic properties were studied. Results： The recombinant plasmid pET28a-gadA was successfully constructed， which was demonstrated by PCR and double restriction endonuclease-digested analysis. The SDS-PAGE analysis showed that glutamate decarboxylase A obtained by Ni2+ affinity chromatography was electrophoretically pure， and its specific activity and recovery rate were respectively 19 U/mg and 12.8%. The activity of glutamate decarboxylase A was the highest at pH 4.5， and its optimal temperature was 50 ℃. It was stable at 40 ℃ and was unstable at 70 ℃. Only 17.9% of the original activity was retained at 70 ℃ for 150 min. Cu2+ had a strong inhibition to the activity of glutamate decarboxylase A， and Ba2+， Co2+ and Mg2+ had not obvious influence on its activity， while Ca2+ could significantly enhance its activity. Conclusion： This study lays a foundation for deeply understanding enzymatic properties of glutamate decarboxylase A and for the preparation of γ-aminobutyric acid.