To reveal the genetic diversity of Oratosquilla oratoria from Yellow Sea, genetic variations among six populations were studied by molecular markers. A total of 39 haplotypes and 41 variable sites were defined in 627 sites for 72 COⅠ sequences. The average values of nucleotide diversity and haplotype diversity were 0.005 12 and 0.962 5, respectively. Genetic distance among populations ranged from 0.004 3 to 0.006 4. High genetic diversity was found in Yancheng population, but the lower nucleotide diversity was discovered in Qingdao and Rizhao populations. Results of mismatch distribution, Tajima’s D statistics (Tajima’s D=-2.051 69,P<0.05) and Fu’s F test (Fu’s Fs=-40.079) supported a sudden population expansion event. The time of expansion was estimated to occur about 55 000 years ago by τ value and molecular clock. The results could provide a scientific basis for protection and utilization of germplasm resources of O.oratoria in Yellow Sea.