Cytochrome c oxidase subunit II gene(CO gene) is subunit of cytochrome oxidase, which is complex IV of mitochondria electron transport system. It has been frequently used in molecular phylogenetic studies because the speed of its DNA variation is faster than that of nucleus. It is especially useful in phylogenetic study of molecular biology in insects. In this study, we cloned and sequenced CO gene of mitochondria DNA from Rhabditidae family nematode. Our results showed that this gene is comprised of 696 base pairs(bp). In the analysis of similarity of this gene with other known genes of 14 species of nematodes in Rhabditida order, we identified that this gene has high similarity with that of Caenorhabditis briggsae(86.0%) and C. elegans(85.6%) in Rhabditidae family. On the meanwhile, it has very low similarity with that of Angiostrongylus cantonensis(31.8%) in Angiostrongylidae family and Metastrongylus salmi(31.6%) in Metastrongylidae family. Based on the results of this study, we suggest that this nematode is closely related with that of Caenorhabditis genus in Rhabditidae family.