Objective:To explore the effects of rosmarinic acid (RA) on the tubular epithelial-mesenchymal transition by aldosterone (ALD) and its possible mechanisms in vitro. Methods:HK-2 cells were divided into five groups:normal group,HK-2 cells induced by ALD,ALD+RA (5 μg/ml),ALD+RA (25 μg/ml),ALD+rotenone(ROT,10 μmol/L). The morphology of transdifferentiate tubular cells was observed using phase-contrast-microscopy. E-cadherin,Vimentin,α-SMA and ERK1/2 were determined by semi-quantitative RT-PCR and Western blot;Reactive oxygen species(ROS) was detected by fluorescence microscopic and fluorescence elisa. Results:HK-2 cells induced by ALD converted into spindle shape from typical epithelium shape,the expression of Vimentin,α-SMA,phosphor-ERK1/2 and ROS production was significantly increased,the expression of E-cadherin was significantly decreased;compared with ALD treated groups,RA (5 μg/ml,25 μg/ml) and mitochondrial respiratory chain complex I inhibitor rotenone (ROT,10μmol/L) significantly inhibited ROS generation,vimentin,α-SMA and phosphor-ERK1/2 expression,and E-cadherin expression was restored. Conclusion:RA inhibited ALD-induced EMT via blocking mitochondrial-originated,ROS-dependent ERK1/2 activation.