Histidine kinase CpxA, a kind of membrane protein, is a pivotal member in Cpx two-component regulatory systems, which consist of CpxA, CpxR, and CpxP. Of those, CpxA is the most important part with the function of acting as sensor kinase. In order to clarify the specific mechanism of CpxA in Cpx system, some experiments must be carried out in vivo and in vitro, so the urgent problem is to express the CpxA protein in vitro. In this study, therefore, cpxA gene from Pectobacterium carotovorum subsp. carotovorum was cloned and inserted into pET-15b plasmid, and the recombinant plasmid (pET-15b/cpxA) transformed into BL21 (DE3). Additionally, the cpxA gene was expressed through the induction of IPTG, under the control of lac promoter.