The fat greenling (Hexagrammos otakii) is one of the most important commercial fishes found along northern coast of China, with fast growth rate, high nutritional value and wide consumer acceptance. In recent years, large-scale proliferation and release activities have been held to restore its natural resources. In order to analyze the genetic diversity and genetic differences between releasing population and natural population of H. otakii, mitochondrial DNA control region and four microsatellite markers were selected for assessment. Mitochondrial DNA control region results showed that the length of the first hypervariable region was 436 bp, and 117 haplotypes were observed in 413 H. otakii individuals, among which only Hap_3, Hap_7, Hap_17 were shared by different populations. Number of individuals in releasing population and wild population was 74 and 105, accounting for 46.54% and 41.34% respectively, and the nucleotide diversity in releasing population and wild population was 0.005 1-0.006 7, 0.005 8-0.007 5, while the haplotype diversity was 0.856 7-0.949 9 and 0.883 1-0.954 9, respectively. Both of them showed a high level of genetic diversity for releasing and wild populations. Microsatellite markers results showed that the average allele number (N_a) was 13-44, 13-27, and the average polymorphism information content (PIC) was 0.885 6, 0.874 0, respectively, which indicated that genetic polymorphism of releasing and wild population was moderately high; results of population genetic structure analysis showed that the genetic differentiation between released population and wild population was smaller, i.e. ata lower genetic differentiation level. In summary, rich genetic diversity existed in both populations, and there was no significant population differentiation in genetic structure, which indicates that the proliferation and release activities have no obvious genetic diversity impact on the wild population.