Objective To study the value of plasma level of matrix metalloproteinase-9 (MMP-9) for the early diagno-sis of Kawasaki disease. Methods The difference in MMP-9 level was studied by retrospective nested case-control method between children with early Kawasaki disease, Henoch-Sch?nlein purpura (HSP) or respiratory infection, and healthy control children. The associations of MMP-9 with serum procalcitonin, erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) were also analyzed. The cutoff-value, sensitivity and speciifcity of MMP-9, ESR and CRP in diagnosis of Kawasaki disease were studied by ROC curve. The areas under ROC curves were compared among different diagnostic markers to deter-mine their signiifcances in diagnosis of Kawasaki disease. Results The plasma level of MMP-9 was increased in early phase of Kawasaki disease, and higher than that in children with HSP or respiratory infections and in healthy controls (P<0.05). If MMP-9, ESR and CRP cutoff value were set to be 90.23 ng/ml, 56.5 mm/h and 27.55 mg/L, the sensitivity, speciifcity and area under ROC curve was 83.3%, 86.4%and 0.904, 95.8%, 66.1%and 0.807, 83.3%, 74.6%and 0.789 respectively. The diagnostic performance of MMP-9 for Kawasaki disease was better than that of ESR and CRP. Conclusions The plasma level of MMP-9 is increased in the early stage of Kawasaki disease. The sensitivity and speciifcity of MMP-9 in diagnosis of Kawasaki disease are highest if cutoff value is set to be 90.23 ng/ml.