MicroRNAs (miRNAs) can regulate proliferative status of pulmonary artery smooth muscle cells (PASMCs), which is a core factor modulating pulmonary vascular remodeling diseases, such as atherosclerosis and pulmonary arterial hypertension (PAH). Our previous work has shown that miR-4632, a rarely reported miRNA, is significantly downregulated in Platelet-Derived Growth Factor (PDGF)BB-stimulated human pulmonary artery smooth muscle cells (HPASMCs), yet its cell function and the underlying molecular mechanisms remain to be elucidated. Here, we find that miR-4632 is highly expressed in HPASMCs and its expression significantly decreased in response to different stimuli. Functional studies revealed that miR-4632 inhibited proliferation and promoted apoptosis of HPASMCs, but had no effects on cell contraction and migration. Furthermore, the cJUN was identified as a direct target gene of miR-4632, while knockdown of cJUN was necessary for miR-4632-mediated HPASMCs proliferation and apoptosis. In addition, the downregulation of miR-4632 by PDGFBB was found to associate with histone deacetylation through the activation of PDGFR/PI3K/HDAC4 signaling. Finally, the expression of miR-4632 was reduced in serum of patients with PAH. Overall, our results suggest that miR-4632 plays an important role in regulating HPASMCs proliferation and apoptosis by suppression of cJUN, providing a novel therapeutic miRNA candidate for the treatment of pulmonary vascular remodeling diseases. It also implies that serum miR-4632 has the potential to serve as a circulating biomarker for PAH diagnosis.