Objective To explore the diagnostic value of a disintegrin-like and metalloproteinase with thrombospondin type 1 motifs (ADAMTS)-9 in acute aortic dissection (AAD). Methods A total of 328 patients with acute onset of chest pain within 24 hours were enrolled in West China Hospital from January 2015 to June 2016 and according to the results of computed tomography angiography they were divided into an AAD group (n=172, 107 males, 65 females, mean age of 50.4±13.1 years) and a control group (n=156, 89 males, 67 females, mean age of 54.9±14.7 years). The enzyme-linked immunosorbent assay (ELISA) test was used to measure the level of ADAMTS-9. Results Patients in two groups had no significant difference in age, gender, smoke history, hypertension history, total cholesterol, triacylglyceride and hemoglobin (P>0.05). But systolic and diastolic blood pressures were significantly higher in the AAD group than those in the control group (P<0.05, respectively). The level of ADAMTS-9 was significantly higher in the AAD group than that in the control group (249.4±186.8 ng/mlvs. 78.2±48.6 ng/ml,t=11.107, P<0.001). Receiver operating characteristic curve analysis showed that ADAMTS-9 (156.7 ng/ml) was predictive in the diagnosis of AAD with sensitivity of 0.942 and specificity of 0.628. Conclusion ADAMTS-9 might be an effective and important biomarker in diagnosis of AAD.