It has been reported that osteoporosis induced by the deficiency of estrogens in menopause is associated with the unbalance of Ca²⁺ and Pi levels. Proximal tubule is very important organ to regualte Ca²⁺ and Pi level in the body. However, the effect of estrogens on Ca²⁺ and Pi regulation was not elucidated. Thus, we examined the effect of 17-β estradiol (E₂) on Ca²⁺ and Pi uptake in the primary cultured rabbit renal proxiaml tubule cells. In the present study, E₂(> 10^-9M) decreases Ca²⁺uptake and stimulates Pi uptake over 3 days. E₂-induced decrease of Ca²⁺ uptake and stimulation of Pi uptake were blocked by actinomycin D (a gene transcription inhibitor), cycloheximide (a protein synthesis inhibitor). tamoxifen, and progesterone (estrogen receptor antagonists). E₂-induced decrease of Ca²⁺ uptake and stimulation of Pi uptake were blocked by SQ22536 (an adenylate cyclase inhibitor), Rp-cAMP (a cAMP antagonist), and PKI (a protein kinase A inhibitor). Indeed, E₂ increased cAMP formation. In addition, E₂-induced decrease of Ca²⁺ uptake and stimulation of Pi uptake were blocked by staurosporine, H-7, and bisindolylmaleimide I (protein kinase C inhibitors) and E₂ translocated PKC from cytoslic fraction to membrane fraction. In conclusion, E₂ decreased Ca²⁺ uptake and stimulated Pi uptake via cAMP and PKC pathway in the PTCs.