The medicinal herb, Panax notoginseng, has been used for thousands of years in traditional Chinese medicine and possesses anti-fibrosis properties. Epithelial-myofibroblast transition (EMT) plays an important role in renal tubulointerstitial fibrosis. The present study was designed to examine whether ginsenoside Rg1, a major active component isolated from Panax notoginseng, has an ability to block this phenotypic transition in rat renal tubular epithelial cells (NRK-52E) induced by transforming growth factor-beta1 (TGF-beta1). The morphology of tubular epithelial-myofibroblast transition was observed through light microscope and transmission electron microscopy. alpha-SMA and E-cadherin are two markers of tubular epithelial-myofibroblast transition, their protein expressions were assessed by immunohistochemistry and western blot analysis. Gene expression of alpha-SMA as well as the two major extracellular matrix components collagen I and fibronectin was measured by real-time PCR analysis. Enzyme-linked immunosorbent assay was used to quantitatively detect collagen I and fibronectin in the supernatant. Our results revealed that ginsenoside Rg1 obviously blocked morphologic transformation in NRK-52E induced by TGF-beta1. Meanwhile, ginsenoside Rg1 inhibited the expression of alpha-SMA and the loss of E-cadherin, subsequently decreased the levels of collagen I and fibronectin in a dose-dependent manner. In addition, western blot analysis indicated that ginsenoside Rg1 inhibited the expression of P-ERK1/2 in NRK-52E induced by TGF-beta1. These results suggest that ginsenoside Rg1 can restrain the process of EMT maybe via suppressing the expression of P-ERK1/2 in vitro.