Commonly known as mantis shrimps, stomatopods are commercially valuable and taxonomically diverse. In spite of high species diversity, stomatopod species exhibit subtle morphological differences, which make species identification a difficult task based on taxonomic keys alone. DNA barcoding has been proposed as a promising tool for species identification and discovery in a wide range of animal taxa. In this study, the performance of DNA barcoding in delineating stomatopod species in the China seas was assessed. The nucleotide sequences of mitochondrial cytochrome oxidase subunit-I (COI) gene were obtained from 204 individuals of 38 stomatopod species in 24 genera in a wide phylogenetic range. These 204 sequences were compared with the other 42 homologous sequences from 14 species of Stomatopoda retrieved from GenBank. Sequence comparisons revealed 223 polymorphic sites, 217 of which were parsimony informative, and no InDels were found. The COI sequences showed a strong AT bias (63.5%) in nucleotide composition. As expected, the mean Kimuara-2-parameter (K2P) genetic divergence increased with an increase in the taxonomic rank. The pairwise genetic divergences among conspecific individuals ranged from 0% to 3.91%, with a mean of 0.76%. The mean K2P pairwise divergence between individuals of congeneric species was 12.91%, ranging from 6.55% to 18.99%. The mean K2P pairwise divergence between individuals of different genera that belong to the same family was 16.89% (range 9.16%-23.32%), and mean K2P pairwise divergence between individuals of different stomatopod families was 21.31% (range 16.52%-26.6%). Thus, an obvious "barcoding gap" was found between intraspecific and interspecific divergences of COI sequences within Stomatopoda. The neighbor-joining phylogenetic tree reconstructed by COI sequences recovered most species as monophyletic with high bootstrap support, except for the species represented by a single individual. In addition, two reciprocally monophyletic, highly supported lineages together with large inter-lineage relative to intra-lineage divergences recovered from COI data concur in suggesting the existence of two possible cryptic species in (De Haan, 1844). These results demonstrate the effectiveness of mitochondrial COI-based DNA barcoding for species identification and cryptic discovery in stomatopods.