Objective To explore the roles of Salvia Miltiorrhiza Bge (SMB) in improving myocardial fibrosis in aged spontaneously hypertensive rats and the possible mechanisms —— cyclooxygenase pathway of arachidonic acid. Methods The 17-month-old SHR rats were given consecutive SMB injection or saline control for 12 weeks, while the age-matched WKY rats were selected as normal control. Meanwhile, celecoxib, the specified arachidonic acid cyclooxygenase-2 (COX-2) inhibitor, was administrated intragastrically before SMB injection. The blood pressure, hemodynamic index and left ventricular mass index were determined. HE staining and Masson staining were performed to analyze the size of myocardial cells or the level of myocardial fibrosis, as well as left ventricular myocardial expression and activity level of COX-2 protein. Results Compared with the elderly WKY rats, senescent SHR had higher blood pressure[systolic blood pressure: (171±12) vs (125±3)mmHg; diastolic blood pressure: (115±9) vs (87±3)mmHg; mean artery pressure: (139±10) vs (106±5)mmHg , P＜0.05], deterious heart function[LVEDP: (13.9±1.7) vs (7.6±1.3)mmHg; LVdP/dtmax: (2528±167) vs (3015±217)mmHg/s; ?LVdP/dtmax: (1957±134) vs (2501±175)mmHg/s, P＜0.05], increased left ventricular mass index[(3.45±0.07) vs (2.23±0.06)mg/g, P＜0.05], increased myocardial cells[diameter: (23.5±0.4) vs (14.3±0.4)μm, P＜0.05], severe fibrosis[myocardial interstitial fibrosis index: (1.66±0.05)% vs (0.64±0.05)%; myocardial perivascular fibrosis index: (139±9)% vs (68±7)%, P＜0.05], elevated expression[(125.8±7.2) vs (47.6±3.8), P＜0.05] and activity level of myocardial COX-2 protein[(73.9±5.6) vs (56.7±4.4)kU/g, P＜0.05]. Except the systolic blood pressure, other indicators in SMB-treated SHR were significantly reduced. The administration of celecoxib partially abolished the effect of SMB. Conclusion SMB therapy can reverse myocardial fibrosis in senescent spontaneously hypertensive rats, which may be through cyclooxygenase pathway.