Objective:To determine whether effects of active vitamin D deficiency and subsequent alterations of milk contents on tooth and mandible development in sucking pups. Methods:Comparison of tooth and mandible phenotypes between 25-Dihydroxyvi-tamin D3 1α-hydroxylase heterozygous[1α(OH)ase+/-] and homozygous[1α(OH)ase-/-] sucking mice at 2-week-old fed by 1α(OH)ase+/- or 1α(OH)ase-/- dames by radiography,micro-CT and histology. Results:Milk calcium levels were decreased in 1α(OH)ase-/- dames compared with that in 1α(OH)ase+/- dames. Dental volume and bone volume in mandibles were reduced in 1α(OH)ase-/- pups compared with those in their 1α(OH)ase+/- littermates. Dental volume and bone volume in mandibles were also reduced in pups fed by 1α(OH)ase-/ dames compared with pups fed by 1α(OH)ase+/- dames. Dental volume and bone volume in mandibles were the highest in 1α(OH)ase+/- pups fed by 1α(OH)ase+/- dames and were lowest in 1α(OH)ase-/- pups fed by 1α(OH)ase-/- dames. Conclusion:Active vitamin D and high milk calcium intake stimulate the mineralization and development of teeth and mandibles respectively and have cooperative action.