Peroxisome proliferator-activated receptor-gamma (PPAR)-gamma is a ligand-activated transcriptional factor belonging to steroid receptor superfamily. PPAR-gamma plays a role in both adipocyte differentiation and tumorigenesis. Up to date, PPAR-gamma is expressed in various cancer tissues, and PPAR-gamma ligand induces growth arrest of these cancer cells. In this study, we examined the expression of PPAR-gamma in prostate cancer (PC) and testicular cancer (TC) by RT-PCR and immunohistochemistry, and we also examined the effect of PPAR-gamma ligand in these cells by MTT assay, hoechest staining, and flow cytometry. PPAR-gamma expression was significantly more extensive and intense in malignant tissues than in normal tissues. PPAR-gamma ligand induced the reduction of malignant cell viability through apoptosis. These results demonstrated that the generated PPAR-gamma in PC and TC cells might play an important role in the tumorigenesis. PPAR-gamma may become a new target in the treatment of PC and TC.