We studied the population structure of cotton bollworm (CBW), Helicoverpa armigera (Hübner) (Lepidoptera:Noctuidae), in Xinjiang, the largest cotton-growing region in China, using a fragment of cytochrome c oxidasesubunit I (COI) gene. Alignments of all 192 COI sequences revealed 28 haplotypes including 23 in southernXinjiang, 5 in eastern Xinjiang and 13 in northern Xinjiang. Negative and significant values of neutrality tests forthe Tajima's D and Fu's FS parameters, combined with the high values of haplotype diversity (Hd), low values ofnucleotide diversity (π) and a high number of low frequency haplotypes indicated a recent demographic expansionof Xinjiang CBW populations. Analysis of molecular variation (AMOVA) indicated low and non-significantgenetic structure, regardless of geographical scale or crop, with most of genetic variation occurringwithin local CBW populations. Pairwise FST analyses also indicated low genetic differentiation. This demographicevent and high gene flow could be responsible for the low genetic structure currently found. CBW populations inXinjiang need to be considered as one panmictic unit in its management, especially for the design of refuges todelay the development of resistance by this migratory pest to transgenic Bt (Bacillus thuringiensis) cotton.