Concentration-mortality response bioassays were conducted in 2021 to define the toxicity of afidopyropen to field populations of cotton aphids, Aphis gossypii Glover (Hemiptera: Aphididae), in Xinjiang region, China. Levels of activity of selected enzymes also were measured. Varying levels of resistance to afidopyropen were detected among aphids from nine major cotton-growing areas in the region. Higher resistance levels were detected in aphids collected from Tumshuk, Alar, and Kurle, with resistance ratios of 4.570, 2.058, and 1.565, respectively. Lower resistance ratios of 0.506, 0.632, and 0.775 were detected in aphids collected from Yinli, Wujiaqu, and Hami, respectively. Biochemical assays showed a highly significant positive correlation of the detoxifying enzymes carboxylesterase and multifunctional oxidase with the level of tolerance, with enzyme activity increasing with the level of tolerance. Glutathione S-transferases and acetylcholinesterase activity in field-collected aphids differed significantly from laboratory colony populations, but their activity did not differ among the field populations. We concluded that cotton aphids in major cotton areas of Xinjiang have not yet developed resistance to afidopyropen and remain sensitive to afidopyropen as indicated by resistance ratios of <5; however, resistance of cotton aphids to afidopyropen in southern Xinjiang is higher than that detected in cotton aphid populations in northern Xinjiang.