In this study, we demonstrate an important role of activation of the hypoxia-inducible factor-1 (HIF-1) pathway in endometrial carcinogenesis and tumor phenotype development of endometrial carcinoma, and suggest a unique role of the HIF-1-target gene, differentiated embryo chondrocyte 2 (DEC2), in carcinogenesis. Hypoxia caused an increase in HIF-1alpha protein expression in 4 endometrial carcinoma cell lines. The expressions of its 5 target genes - DEC1, DEC2, carbonic anhydrase-9 (CA9), vascular endothelial growth factor (VEGF), and solute carrier family 2, member 1 (SLC2A1) - also reactively increased in most of the cell lines, except for DEC2 in the SNG-M cells. The expression levels of DEC2, CA9, and SLC2A1 were significantly higher in the 4 atypical hyperplasia tissues and 82 endometrial carcinomas compared with those in the 21 normal endometria. Clinicopathological analyses of carcinoma patients revealed a significant correlation of the VEGF and SLC2A1 expression with the status of lymph-vascular involvement and lymph node metastasis. The expression levels of CA9 and VEGF were significantly higher in the tumors of post- as opposed to pre-menopausal patients. The SLC2A1 expression was also related to the FIGO stage, but the DEC2 expression was inversely related to the FIGO grade. The activation of the HIF-1 pathway could be related to endometrial carcinogenesis, and the component, DEC2, could have different expression-regulatory mechanisms and unique roles in carcinogenesis.