Abstract: MicroRNA-21(miRNA-21), a kind of small endogenous non-coding RNA, is widely expressed in various tissues and plays a pivotal role in the occurrence and development of many diseases. In recent years, the role of miRNA-21 in pulmonary hypertension(PH) has attracted extensive attention, and its function in subtypes of PH is not always the same or even contradictory. This review summarized recent advances of miRNA-21 in PH, encompassing pathophysiological processes mediated by miRNA-21, its roles in subtypes of PH, and insufficiency of current researches, in order to figure out the role of miRNA-21 in PH and provide a reference for future studies.