Abstract: The aim of this study was to investigate the taxonomic relationships of ascarid nematodes from Ailuropoda melanoleuca, Ailurus fulgens, Ursus maritimus, Ursus arctos pruinosus, Ursus thibetanus mupinensis, Ursus arctos lasiotus, Pan troglodytes and Hylobates hoolock. The mitochondrial cytochrome coxidase subunitsⅠ(COXⅠ) and Ⅱ (COXⅡ) were amplified by PCR and sequenced directly. Then, sequence analyses was carried out based on COXⅠ and COXⅡ sequences from ascarid nematodes acquired in our study and 12 homologous sequences from GenBank. The lengths of COXⅠ and COXⅡ in ascarid nematodes from the eight species of captive animals were all 393 bp and 582 bp, respectively. The COXⅠ and COXⅡ of ascarid nematodes from giant panda shared 94.8%-95.0% and 94.9%-95.5% sequence identity with these from A. fulgens, U. maritimus, U. arctos pruinosus, U. thibetanus mupinensis and U. arctos lasiotus, respectively. Additionally, the COXⅠand COXⅡ genes of ascarid nematodes from P. troglodytes shared 99.8% and 99.5% identity with the nematodes from H. hooloc, respectively. Phylogentic analysis showed that ascarid nematodes from A. melanoleuca, A. fulgens and four Ursids species belonged to the genus Baylisascaris, while roundworms from H. hoolock and P. troglodytes clustered under the genus Ascaris. These results showed that a co-evolutionary relationship may link the ascarid nematodes and their corresponding hosts together.