Japanese foxtail is one of the most common and competitive annual grass weeds of wheat in China. Whole-plant dose-response experiments were conducted with fenoxaprop and pinoxaden to confirm and characterize resistant and susceptible Japanese foxtail populations and to elucidate the basis of resistance to these herbicides. The resistant Japanese foxtail population was 49-fold resistant to fenoxaprop and 16-fold (cross) resistant to pinoxaden relative to the susceptible population, which was susceptible to both fenoxaprop and pinoxaden herbicides. Molecular analysis of resistance confirmed that the Ile1781 to Leu mutation in the resistant population conferred resistance to both fenoxaprop and pinoxaden. This is the first report of cross resistance of Japanese foxtail to pinoxaden in the world and of a target site mutation that corresponded to resistance to both fenoxaprop and pinoxaden in Japanese foxtail. Prior selection pressure from fenoxaprop could result in evolution of resistance to fenoxaprop and cross resistance to pinoxaden in Japanese foxtail population.