Ochetobius elongatus used to be an economically important fish species in many rivers of China.However,due to environmental destruction and human disturbance the resources of this fish species have reduced rapidly,and its populations are in a critically endangered condition.At present,it is very difficult to obtain specimens of O.elongatus,which limits research on this species.We obtained specimens of O.elongatus via larva and adult fish collection.Two mitochondrial genes and two nuclear genes were used to explore the genetic diversity and population demography of O.elongatus in middle and lower Xijiang River.Results showed that the genetic diversity of O.elongatus was low and is in recession,suggesting that O.elongatus might have undergone a genetic bottleneck event.Additionally,population demographic analyses revealed that O.elongatus population expanded during the Late Pleistocene (0.06 and 0.13 Million years ago),following the glacial retreat of the Middle Pleistocene glaciations (0.78-0.126 Million years ago).The results also revealed that Pleistocene climatic fluctuations have influenced the population demography of O.elongatus.Due to its potential as an important spawning ground for O.elongatus,sections of middle and lower Xijiang River should be considered as candidates for creating nature reserves to conserve and restore its genetic resources.