Abstract： Objective To explore the clinical efficacy of allogenic mesenchymal stem cells transplantation (MSCT) in patients with refractory polymyositis/dermatomyositis (PM/DM). Methods Bone marrow derived mesenchymal stem cells (BM-MSC) or umbilical cord derived mesenchymal stem cells (UC-MSC)were infused intravenously in 8 PM/DM patients. The clinical manifestations and laboratory parameters,including serum creatin in kinase (CK) and manual muscle test 8 (MMT8) score, were compared before and after MSCT. Staistically andlyzed by paired t-test. Results The eight patients were followed up for six to twelve months after MSCT. The level of serum CK decreased from (1681±430) to (886±248) U/L one week after MSCT (P＜0.05) and further decreased at week 2 (474±61) U/L, 1 month (293±89) U/L, 3 month (202±70) U/L and 6 month (175±46) U/L, respectively (all P＜0.05). MMT8 score increased to 1 month [(67±3) vs (45±14), P＜0.05], 3 month [(64±10) vs (45±14), P＜0.05], 6 month [(64±4) vs (45±14),P＜0.05] after MSCT. The dosage of glucocorticoid steroid were tapered in all patients 2 weeks after MSCT [(18±6) mg vs (34±15) mg, P＜0.05]. Clinical symptoms of interstitial pneumonia of both patients were relieved after MSCT, which was confirmed by the result of high resolution CT (HRCT) of the lung.The skin ulcers tended to be recovered after the transplantation in one DM patient. All patients did not develop transplantation related complications. Conclusion Allogenic MSCT is an effective and safe approach for the treatment of refractory PM/DM. However, extensive follow-up study is needed for long-term benefit evaluation.