Many harpins have been found in plant pathogen bacteria that can elicit disease and insect resistance in plants, and promote plant growth. In this work, we overexpressed and purified Xanthomonas oryzae pv. oryzae harpin, harpin(Xoo), in Escherichia coli BL21/pGEX-hpa1. Harpin(Xoo) was fused to the C-terminus of glutathione S-transferase (GST) and purified using the Bulk GST purification module and thrombin cleavage capture kit. Purified harpin(Xoo) protein was sensitive to protease K and stable to heat treatment, and could not induce a hypersensitive response after treatment with various plant metabolic inhibitors; these characteristics were similar to harpin(Ea) of Erwinia amylovora. The purified harpin(Xoo) showed a similar ability to induce tobacco mosaic virus resistance in tobacco as harpin(Ea). Its antibody worked well in detecting the purified harpin(Xoo), harpin(Xoo) in the total protein of E. coli BL21/pGEX-hpa1 and an hpa1 transgenic rice.