Insulin and growth factors activate the phosphatidylinositide (PI)-3kinase-pathway, leading to stimulation of several kinases including the ubiquitously expressed serum- and glucocorticoid-inducible kinase isoform SGK3. This kinase has previously been shown to stimulate a number of transport systems. The present study aimed to define the contribution of SGK3 to the regulation of renal tubular phosphate transport. Coexpression of SGK3 indeed significantly enhanced the phosphate-induced current in NaPi IIa-expressing Xenopus oocytes. To determine the in vivo significance of SGK3-dependent regulation of phosphate transport, SGK3 knockout mice (sgk3^KO) and their wild type littermates (sgk3^WT) were analyzed. Under standard diet, fluid intake, urinary flow rate, glomerular filtration rate, and urinary calcium excretion were similar in sgk3^KO mice and sgk3^WT mice. The fractional urinary phosphate excretion was, however, significantly larger in sgk3^KO than in sgk3^WT mice. Plasma calcium and phosphate concentration were not significantly different between sgk3^KO mice and sgk3^WT mice. Plasma concentration of PTH was similar in both genotypes, but plasma 1,25(OH)₂D₃ was significantly lower in sgk3^KO than in sgk3^WT mice. Bone density was slightly, but significantly lower in sgk3^KO than in sgk3^WT mice. The observations disclose a subtle but significant role of SGK3 in the regulation of renal tubular phosphate transport and bone density.