Genetic diversity, population genetic structure and molecular phylogeographic pattern of mantis shrimp Oratosquilla oratoria in Bohai Sea and South China Sea were analyzed by mitochondrial DNA sequences. Nucleotide and haplotype diversities were 0.00409-0.00669 and 0.894-0.953 respectively. Neighbor-Joining phylogenetic tree clustered two distinct lineages. Both phylogenetic tree and median-joining network showed the consistent genetic structure corresponding to geographical distribution. Mismatch distributions, negative neutral test and "star-like" network supported a sudden population expansion event. And the time was estimated about 44000 and 50000 years ago.