Aim To investigate the role of mineralocorticoid receptor (MR) in myocardial fibrosis of Dahl salt-sensitive hypertensive rats. Methods Dahl salt-sensitive hypertensive rats were treated with high-salt diets or combined with eplerenone (100 mg/kg per day, orally) for 8 weeks. Then measured blood pressure, heart weight/body weight ratios, assessed myocardial fibrosis level by myocardial tissue AZAN staining and quantification of collagen IV mRNA, and also detected the expression of mineralocorticoid receptor protein by Western blot and inflammation related factor in myocardial tissue such as PAI-1 and TGF-β1 mRNA expression by Real Time PCR, then analysied the relationship of the expression of mineralocorticoid receptor and myocardial fibrosis. Results Dahl salt-sensitive rats fed with a high salt diet had increased blood pressure [(168.1±10.8) mmHg vs(124.3±10.2)mmHg]and heart weight/body weight ratio[(0.341±0.006)vs(0.287±0.004)]. The percentage of myocardial fibrosis(11.78%±0.54% vs 3.12%±0.55%)and collagen Ⅳ mRNA(3.23±0.21 vs 1.32±0.06)expression were increased in myocardial tissue. The expression of MR protein and PAI-1,TGF-β1 mRNA were also increased in myocardial tissue, PAI-1 and TGF-β1 mRNA expression were positively related with myocardial fibrosis. Combined with eplerenone in diet, following parameters including blood pressure, heart weight/body weight ratios, myocardial fibrosis level, MR protein, mRNA of collagen, PAI-1 and TGF-β1 were decreased. Conclusion Interaction of MR and corresponding hormone, can induce inflammatory reaction in heart and result in myocardial fibrosis. MR antagonists can relieve myocardial fibrosis induced by hypertension,and improve myocardial remodeling.