Corosolic acid (CRA) is a natural compound extracted from leaves of Banaba and exerts anti-inflammatory, anti-diabetic, anti-hyperlipidemic, anti-oxidant, and anti-tumor effects. We have recently demonstrated that CRA inhibits the expression of STAT3 and ameliorates the development of pulmonary arterial hypertension (PAH). In the present study, we focused on platelet-derived growth factor receptor (PDGFR) signaling, which enhances in PAH patients, and examined the downregulating mechanism of STAT3 expression by CRA. The expression level of PDGFRβ was higher in pulmonary arterial smooth muscle cells (PASMCs) from idiopathic pulmonary arterial hypertension (IPAH) patients than in normal PASMCs. Increased expression of PDGFRβ in IPAH-PASMCs was reduced by the treatment with CRA in a time-dependent manner. The expression of two downstream pathways of PDGFRβ signaling, STAT3 and NF-κB, was also upregulated in IPAH-PASMCs, which was attenuated by CRA. In addition, the phosphorylation levels of PDGFRβ and STAT3 were reduced by CRA. The excessive proliferation and migration of IPAH-PASMCs following PDGF stimulation were inhibited by CRA. In conclusion, CRA inhibits the development of PAH via the downregulation of PDGFRβ-STAT3 and PDGFRβ-NF-κB signaling pathways.