Abstract: Objective：To explore the effect of knockout of Acvr1（activin A receptor type 1） on the formation of dentin. Methods： Acvr1 conditional knockout mice model was constructed using Cre-loxP system. The genotype Osterix-Cre; Acvr1fx/- was chosen as the experiment group and the genotype Osterix-Cre; Acvr1fx/+ was chosen as the control group in littermate. We observed the dentin formation and odontoblast morphology by imageology and HE staining. And we checked the expression of the odontoblast/osteoblast markers by immunohistochemical staining. Finally the expression of odontoblast/osteoblast genes was detected by qRT-PCR. Results：The mandibles of the experiment group showed more pores, the dentin of mandibular first molar was thinner, pre-dentin was thicker, and odontoblast looked irregular. The genes important for odontoblast differentiation such as Dspp, Nestin were downregulated. However, the incisor showed osteodentin, and the Dspp was down-regulated. IHC showed down-regulated DSPP in cKO molar. Conclusions：ACVR1 affected the formation of dentin by up-regulating odontoblast differentiation, and also had important role in odontoblast transition.