What is the central question of this study?Thoracic aortic aneurysm and dissection (TAAD) is characterized by extracellular matrix remodelling and an inflammatory response. Evidence suggests that ADAMTS1 is closely associated with TAAD development, but whether it contributes to the pathophysiology of TAAD remains unknown. What is the main finding and its importance?We generated inducible postnatal ADAMTS1 knockout mice and found that ADAMTS1 deficiency attenuated beta-aminopropionitrile-dependent TAAD formation and rupture. Furthermore, ADAMTS1 deficiency suppressed neutrophil and macrophage infiltration by inhibiting inflammatory cytokine levels and macrophage migration during the early stage of beta-aminopropionitrile-induced TAAD. ADAMTS1 could be a new therapeutic target for TAAD. Thoracic aortic aneurysm and dissection (TAAD), as a life-threatening cardiovascular disease, is characterized by extracellular matrix remodelling and an inflammatory response. A disintegrin and metalloproteinase with thrombospondin motifs 1 (ADAMTS1) is an inflammation-related protein that is able to degrade extracellular matrix proteins in arteries. Herein, we investigated whether ADAMTS1 contributes to the pathophysiology of TAAD in mice. Using the mouse model of beta-aminopropionitrile (BAPN)-induced TAAD, we found that ADAMTS1 expression was upregulated beginning in the early stage of TAAD development and localized predominantly in the aortic adventitia. ADAMTS1-floxed mice and whole-body tamoxifen-inducible ADAMTS1 knockout mice (ADAMTS1(flox/flox) Ubc-Cre(ERT2+), ADAMTS1 KO) were generated to investigate the direct causal role of ADAMTS1 in TAAD development. The incidence and rupture rates of BAPN-induced TAAD in ADAMTS1 KO mice were significantly lower than those in ADAMTS1(flox/flox) mice (45.5 versus 81.8% and 18.2 versus 42.4%, respectively). Aortas from BAPN-treated ADAMTS1(flox/flox) mice displayed profound destruction of the elastic lamellae, abundant neutrophil and macrophage accumulation in the adventitia, obviously increased neutrophil proportions in peripheral blood and significantly increased expression of inflammatory factors in the early stage of TAAD induction, all of which were markedly suppressed in ADAMTS1 KO mice. Furthermore, ADAMTS1-deficient macrophages exhibited abrogated migration capacity both in vivo and in vitro. In conclusion, ADAMTS1 plays a crucial role in postnatal TAAD formation and rupture by regulating inflammatory responses, suggesting that ADAMTS1 might be a new therapeutic target for TAAD.