Abstract: Objective To analyze the clinical characteristics and laboratory data of Adult-onset Still's Disease(AOSD) complicated with macrophage activation syndrome(MAS). Methods A retrospective analysis of 13 cases of AOSD, complicated by MAS diagnosed in Changhai Hospital of Shanghai from July 2011 to August 2015. Results Among 13 patients, 3 cases were male, 10 cases were female, age(44.1±16.9) years. The main clinical features were fever, high ferritin(more than 2 000 μg/L) with 92% incidence rate(n=12).Rash occurred rate was 85%(n=11) and liver function damage incidence(n=10) 77%, joint pain 54%(n=7), multiple lymph node enlargement of 54%(n=7), incidence of sore throat was 46%(n=6), hepatosplenomegaly incidence rate of 31%(n=4), blood system involvement, anemia incidence rate was 85%(n=11). Blood cells decreased 62%(n=8), when MAS occurs, bone marrow cytology clearly is seen in 3 cases, the treatment of glucocorticoid and CsA delays the disease process. All of the 13 patients were treated with glucocorticoid, 11 cases were treated with cyclosporine, 6 cases were treated with immunoglobulin, 62%(8/13) patients after treatment was alleviated, 5 cases died. The causes of death include mixed infection of the lungs appeared acute cardiopulmonary circulation failure(1 case), interstitial pneumonia associated with infection leaded to respiratory failure(1 case), acute pulmonary edema, heart failure and pulmonary infection after hospital discharge(1 case), multiple organ dysfunction syndrome(1 case), pneumonia associated with infection leaded to respiratory failure(1 case). Conclusion It indicates that MAS complicated when AOSD has high fever, ESR and fibrinogen decreased. Guarding against that infection is the cause of AOSD to induce MAS. Glucocorticoid combined with IVIG and CsA can control the disease development.