Objective The dentate gyrus has an important role in learning and memory, and adult neurogenesis in the subgranular zone of the dentate gyrus (DG) may play a role in the acquisition of new memories.Previous studies have shown the forkhead box G1(foxgl) transcription factor is strongly expressed in the developing DG.Methods To elucidate its role in postnatal DG development, we generated afoxgl fox/flox mouse line and an inducible Cre mouse line Frizzled9-CreERTM.As for the Frizzled9-CreERTM line, Cre-mediated recombination was strongly detected in the hippocampal primordium and its derivatives at embryonic stages.From P2 to adult, recombinase activity was still highly detected in DG, making this line a useful tool to study DG development.With the two lines of Frizzled9-CreERTM and foxglflox/flox crossed, combining with tamoxifen induction, foxgl was conditionally deleted in DG at postnatal developing stages.Results Inactivation of FoxG1 at postnatal day 5 led to remarkable malformation of the DG: (1) The DG showed a drastically shrinking size with a loss of lower blade, and the secondary radial glial scaffold was severely disrupted; (2) Detailed scrutiny revealed thatfoxgl was necessary for the maintenance of the progenitor pool.Lack offoxgl promoted both gliogenesis and neurogenesis; (3)foxgl stimulates survival and maturation of postmitotic neuron; (4) Some IPC and postmitotic neuron exhibited glial-shape and express astrocytic marker, indicating a lineage transition from neuron toward astrocyte inducing byfoxgl inactivation.Conclusion In summary, our results suggested thatfoxgl is critical for postnatal DG development.