Todarodes pacificus(T. pacificus) is an important fishery species around the world. In order to scientifically manage and exploit this fishery resources, mitochondrial COⅠgene and Cytb gene sequences were assessed to explore the level of genetic structure and variation of T. pacificus from the northwestern Pacific Ocean.465 bp(COⅠ) and 404 bp(Cytb) gene sequences were obtained and a total of 18 and 21 haplotypes were defined, which had been derived from 90 individuals in three sites. The results showed that the haplotype diversity of COⅠ gene and Cytb gene sequences were 0.493 and 0.479, respectively.The nucleotide diversity of COⅠgene and Cytb gene sequences were 0.001 3 and 0.001 4, respectively. It was also found that genetic differentiation coefficient (F_st) were negtive(F_st<0.05), the tremendous gene flow (Nm) values were approximate infinity. However, molecular biological variance analysis (AMOVA) showed that the genetic variation observed within populations were 100.82% and 99.57%, respectively.There sults of Tajima's D based on COⅠand Cytb gene sequences of T. pacificus were -2.341 2 and -22.643 0 (P<0.01), respectively. In summary, all these results revealed that the genetic diversity of T. pacificus population in the northwest Pacific Ocean was extremely low, and there was no genetic differentiation among the three geographic groups. Besides, the genetic variation mainly came from individuals within the species. And the population expansion occurred about between 12 000 and 15 000 years ago.Therefore, it is suggested that T. pacificus should be regarded as an integration management unit in fishery management.