STARS (STriated muscle Activator of Rho Signaling) is a sarcomeric protein, which expressed early in cardiac development and involved in pathological remodeling. Abundant evidence indicated that STARS could regulate cell proliferation, but it’s exact function remains unclear. In this study, we aimed to investigate the role of STARS in the proliferation of pulmonary arterial smooth muscle cells (PASMC) and the potential effect on the progression of pulmonary arterial hypertension (PAH). In this study, we established a PAH mouse model through chronic hypoxia exposure as reflected by the increased RVSP and RVHI. Western blot and RT-qPCR detected the increased STARS protein and mRNA levels in PAH mice. Next, we cultured the primary PASMC from PAH mice. After STARS overexpression in PASMC, STARS, SRF and Egr-1 were up-regulated significantly. The MTT assay revealed an increase in cell proliferation. Flow cytometry showed a marked inhibition of cell apoptosis. However, STARS silence in PASMC exerted opposite effects with STARS overexpression. SRF siRNA transfection blocked the effects of STARS overexpression in PASMC. In order to further confirm the role of STARS in PAH mice in vivo, we exposed STARS knockout mice to hypoxia and found lower RVSP and RVHI in knockout mice as compared with controls. Our results not only suggest that STARS plays a crucial role in the development of PAH by increasing the proliferation of PASMC through activation of the SRF/Egr-1 pathway, but also provides a new mechanism for hypoxia-induced PAH. In addition, STARS may represent a potential treatment target.