Abstract: Abundant conchostracon fossils were discovered in the Dabeigou Formation at the Zhangjiagou section,Huodoushan Village,Luanping County,Hebei Province.They include4genera and22species.Among these,the species of Nestoria predominate and occur throughout the Dabeigou Formation,so they can be called the Nestoria fauna.In the Dabeigou Formation the authors for the first time found Jibeilim-nadia and Keratestheria,which occur in the lower and upper parts of the formation respectively.The two genera divide the Nestoria fauna into two assemblage zones:the Nestoria-Jibeilimnadia assemblage zone in the lower part and the Nestoria-Keratestheria assemblage zone in the upper part.In addition,the genus cf.Pseudograpta,an important element in the Middle Jurassic Tuchengzi Formation,was for the first time found in the upper part of the Dabeigou Formation at the Zhangjiagou section,which further proves that the conchostracon fauna in the Dabeigou Formation is closely related to that in the Tuchengzi Formation and has great age significance.