Abstract: The cultured populations of Siganus oramin have shown declining economic traits and reduced genetic diversity. To conserve wild germplasm resources, we analyzed mitochondrial Cyt b gene sequences from 197 specimens collected from seven geographic populations along China's southeastern coast (Beibu Gulf-Zhanjiang BB, Wenchang-Hainan WC, Shaba Bay-Yangjiang SB, Dapeng Bay-Shenzhen DP, Daya Bay-Shenzhen DY, Dongshan Bay-Zhangzhou DS, and Sansha Bay-Ningde SS),aiming to assess the genetic diversity status of wild populations.The Cyt b gene sequence was 1 141 base pairs in length, containing 140 variable sites and defining 81 haplotypes. The overall haplotype diversity was 0.921±0.014, and the nucleotide diversity was 0.006 4±0.001 0. The genetic distance and differentiation indexes showed no significant genetic differentiation among the seven populations, and both the neighbor-joining tree and haplotype network structure suggest little genetic differentiation. AMOVA analysis reveals that most variation (99.83%) was found within populations. The results of the neutral test show that the Fu's Fs value was significantly negative (−24.605, p<0.05) and the Bayesian skyline plot analysis reveals that the S. oramin population underwent a demographic bottleneck followed by a rapid population expansion over a short evolutionary time span, which suggests that S. oramin might have experienced a bottleneck effect and population expansion within a short period of time, with the estimated expansion time being about 15.77 thousand years ago.