Abstract: Objective：To observe the expression of three members in the RUNX family, namely RUNX1 ,RUNX2,RUNX3 in mandibular first molars of Balb/c mice at different stages prenatally and postnatally, and explore the mechanism of Runt-related transcription factor in tooth development of Balb/c mice. Methods：The mandibles of Balb/c mice containing mandibular first molars or their germs were isolated at embryonal 19.5 day and postnatal 0、6、14、28 days respectively. The isolated tissues were processed by HE staining and immunohistochemistrical method to detect the expression of RUNX1 ,RUNX2,RUNX3 in tooth development．Results：RUNX1 was detected at E19.5 day in the germs and progressively increased at P 0、6、14、28 days. The expression of RUNX2 was granularly at E19.5 day and P0 day. The lowest point was detected at P6 day, and an uprising positive trend was showed at P14 day and 28 day. Expression of RUNX3 showed a rising trend in dentine at P6、14、28 days but negative at E19.5 day and P0 day. Conclusions：It can be speculated that RUNX1 participates in differentiation of ameloblasts and odontoblasts and maturation of dentine. RUNX2 is mostly correlated with the maturation of dentin．RUNX3 is related to maturation of dentine and formation of tooth shape in later period.