Powdery mildew, one of devastating diseases of wheat worldwide, is caused by Erysiphe graminis f. sp. tritici, a fungal species with constant population changes, which often poses challenges in disease management with host resistance. Transgenic approaches that utilize broad-spectrum resistance may limit changes of pathogen populations and contribute to effective control of the disease. The harpin protein Hpa1, produced by the rice bacterial blight pathogen, can induce resistance to bacterial blight and blast in rice. The fragment comprising residues 10 through 42 of Hpa1, Hpa110-42, is reportedly three- to eightfold more effective than the full-length protein. This study evaluated the transgenic expression of the Hpa110-42 gene for resistance to powdery mildew in wheat caused by E. graminis f. sp. tritici. Nine Hpa110-42 transgenic wheat lines were generated. The genomic integration of Hpa110-42 was confirmed, and expression of the transgene was detected at different levels in the individual transgenic lines. Following inoculation with the E. graminis f. sp. tritici isolate Egt15 in the greenhouse, five transgenic lines had significantly higher levels of resistance to powdery mildew compared with nontransformed plants. Thus, transgenic expression of Hpa110-42 conferred resistance to one isolate of E. graminis f. sp. tritici in wheat in the greenhouse.