Abstract: A new extracellular harpin protein PopW was identified from Ralstonia solanacearum ZJ3721. The expression of recombinant protein PopW could be induced by IPTG, and 0.01 mmol/L was demonstrated to be an optimal concentration for its peak expression. There were significantly less diseased lesions in tobacco leaves treated with PopW followed by the inoculation of TMV than that of control plants, and this induced resistance could last more than eight days with 2.5 mg/L PopW. Moreover, the expression of PR-1a was significantly higher in tobacco leaves treated with PopW than that of control leaves. PopW was also demonstrated to control tomato leaf mold and rice false smut in field with efficiency of 80.19% and 86.84%, respectively. When treated with 2.5 mg/L PopW, pepper planted in field obtained a good yield with an increase of 16.89% compared with the control.