Objective:To determine the role of 1α,25(OH)2D in dentin formation and predentin mineralization of mice. Methods:The differences of the dentin formation and predentin mineralization between the wild-type and 1--琢-hydroxylase gene knockout mice at 6 weeks old were assessed by histology,immunohistochemistry and RT-PCR. Results:The dental volume,the deposition of type I collagen and osteocalcin in tooth matrix, and the expression of osteocalcin in odontoblasts were reduced significantly. But the predentin volume was increased in 1--琢-hydroxylase gene knockout mice compared to that in the wild-type littermates. Conclusion:These studies suggest that 1α,25(OH)2D is essential for the dentin formation and predentin mineralization in mice.