Objective:To determine the simple effect and interaction of parathyroid hormone(PTH) and 1,25(OH)2D3 on the regulation of renal calcium binding proteins. Methods:The expression of renal calbindin D28K and D9K were examined in mice with targeted knockout of the PTH or 1α(OH)ase or both genes by immunohistochemistry. Results:The calbindin D28K and D9K were localized to intracytoplasm of epithelia in the renal cortical distal tubules and medullary collecting ducts. The expression of calbindin D28K and D9K were reduced significantly in kidney in PTH knockout mice, more dramatically decreased in 1α(OH)ase knockout mice and the most dramatically decreased in the double mutant mice. Conclusion:PTH and 1,25(OH)2D3 could play collaborative roles in modulating the expression of calbindin D28K and D9K in the kidney.