Klotho is an anti-aging gene whose expression is regulated by many stimuli. Here we examined the transcriptional regulation of the klotho gene by peroxisome proliferator-activated receptor-gamma (PPAR-gamma). The PPAR-gamma agonists thiazolidinediones increased both klotho mRNA and protein expression in HEK293 cells and several renal epithelial cell lines. The induction was blocked by PPAR-gamma antagonists or small-interfering RNA-mediated gene silencing of PPAR-gamma, suggesting a PPAR-gamma-dependent mechanism. Chromatin immuno-precipitation and gel shift assays found a noncanonical PPAR-responsive element within the 5'-flanking region of the human klotho gene with promoter-reporter assays further confirming transcriptional functionality. Moreover, thiazolidinediones or adenovirus-mediated overexpression of PPAR-gamma increased klotho expression in mouse kidneys while renal klotho expression was attenuated in mice treated with PPAR-gamma antagonists. These results demonstrate that klotho is a target gene of PPAR-gamma.