Objective To observe the morphological changes of principle cells and the expressions of aquaporin（AQP）-2 and AQP-3 in collecting duct during mouse kidney development, so to investigate their relationships and effects. Methods Transmission electron microscopy, immunohistochemistry, Western blotting and stereological methods were used to detect the expressions of AQP-2, AQP-3 and principle cells in mouse kidney of embryonic day 16, 18 and postnatal day 1,3,7,14 and 21. Results The collecting duct principle cells occurred at embryonic day 18. Morphological structures of principle cells were well-developed during postnatal day 7 to 21. AQP-2 was apparently noticed on the apical plasma membrane and in the cytoplasm of principle cells. The expression of AQP-2 increased at postnatal day 1, and reached peak level at postnatal day 21. AQP-3 was expressed on the basolateral membrane of principle cells. The expressions of AQP-3 increased gradually and reached peak level at postnatal day 1. Conclusion AQP-2 and AQP-3 are very important for balance of water during development and maturation in mouse ki