In all, circST6GAL1 deficiency attenuated the migration and proliferation and induced apoptosis in HPASMCs under hypoxia condition in vitro and alleviated pulmonary artery remodeling and PAH in PAH mouse models in vivo via miR‐509‐5p/MCTP2 axis. The gene discussed is MCTP2; the disease is pulmonary arterial hypertension.