Estrogen-related receptor alpha (ERRα), which shares structural similarities with estrogen receptors, is associated with tumor progression in endometrial cancer, but little is known about the detailed underlying mechanism. We investigated whether ERRα, in cooperation with peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α), could participate in epithelial-mesenchymal transition (EMT) in endometrial cancer through cancer-stromal interactions. Two endometrial cancer cell lines, Ishikawa and HEC-1A, transfected with ERRα/PGC-1α expression plasmids or silenced for ERRα expression, were co-cultured with telomerase-transformed human endometrial stromal cells (T-HESCs). We found that EMT-associated factors including vimentin, Snail, and zinc finger E-box binding homeobox 1 were upregulated in cancer cells overexpressing ERRα/PGC-1α and that transforming growth factor-beta (TGF-β) was induced in T-HESCs in the same conditions. In contrast, ERRα knockdown suppressed EMT-associated factors in cancer cells and TGF-β in T-HESCs. ERRα/PGC-1α overexpression increased the expression of EMT-associated factors after TGF-β exposure; however, it decreased E-cadherin at protein level. ERRα knockdown suppressed EMT-associated factors in the presence of TGF-β, whereas E-cadherin remained unchanged. Matrigel invasion assays revealed that ERRα knockdown attenuated the stimulation of migration and invasion by TGF-β. These findings suggest that ERRα is a potential target for inhibiting TGF-β-induced EMT through cancer-stromal interactions in endometrial cancer.