ABSTRACT Beckmannia syzigachne (Steud.) Fernald is one of the main grass weeds severely harming wheat (Triticum aestivum L.) production in rice-wheat areas in China. Fenoxaprop-p-ethyl is the main herbicide used to selectively control grass weed in China. Beckmannia syzigachne has evolved resistance to fenoxaprop-p-ethyl due to continuous application. To investigate fenoxaprop-p-ethyl resistant level and mechanism in B. syzigachne in a portion of the rice-wheat area in China, samples from 31 field populations were collected and treated with fenoxaprop-p-ethyl. The results show that 10 of the 31 tested field populations evolved a high level of resistance to fenoxaprop-p-ethyl. A portion of the acetyl-coenzyme A carboxylase (ACCase) gene was amplified, sequenced and aligned. The known Ile-1781-Leu, Ile-1781-Val, Ile-2041-Asn, Asp-2078-Gly and Gly-2096-Ala mutations were identified in five resistant populations. None of the known resistant substitutions was identified in the other five resistant populations, which means the resistance to fenoxaprop-p-ethyl in these populations is likely endowed by non-target-site resistance mechanism.