Phosphate (P) homeostasis has long been considered to be closely linked with calcium metabolism regulated by calcium-regulating hormones, such as PTH and 1,25-dihydroxyvitamin D(3). The regulation of P is controlled mainly by three factors, absorption in the intestine, redistribution among intracellular, extracellular, and osseous compartments, and reabsorption in the kidney. Renal P reabsorption in the proximal tubule is a key process through sodium-dependent P cotransport, which is regulated mainly by dietary phosphate intake and PTH. Recently, it has been suggested that some putative P-regulating factors might play an important role in the pathogenesis of hypophosphatemic disorders, including TIO, ADHR, and XLH. This review focuses primarily on P regulatory mechanism and some candidates for putative humoral P-regulating factors.