MicroRNA-124 (miR-124) has been reported to be downregulated in the cells exposed to hypoxia, which was confirmed in our study. We then used online microRNA target prediction tools to identify GRB2, SMAD5, and JAG1 as the candidate target genes of miR-124, and we next validated GRB2 as a direct gene by using luciferase reporter system. We also established the regulatory relationship between miR-124 and GRB2 by showing the negative linear relationship between GRB2 and miR-124 expression. Furthermore, we investigated the miR-124 and GRB2 expression levels of different genotypes including CC (n=30), GC (n=18), and GG (n=4), which supported the hypothesis that the presence of minor allele (C) of rs531564 polymorphism compromised the expression of miR-124. Meanwhile, we also conducted real-time polymerase chain reaction and Western blot analysis to study the expression of GRB2 among different genotypes or pulmonary artery smooth muscle cells (PASMCs) treated with miR-124 mimics, GRB2 small interfering RNA, and miR-124 inhibitors, respectively, and found that introduction of miR-124 or GRB2 small interfering RNA could reduce the expression of GRB2 and inhibit the proliferation of PASMCs, while miR-124 upregulated the expression of GRB2 and promoted the proliferation of PASMCs. A total of 412 COPD patients with PAH (n=182) or without PAH (n=230) were recruited in this study, and more individuals carrying at least one minor allele of rs531564 were found in the COPD patients with PAH than in those without PAH (odds ratio: 0.61, 95% confidence interval: 0.41-0.91; P=0.166). In conclusion, the presence of rs531564 minor allele may increase the risk of PAH in COPD by reducing miR-124 expression, increasing GRB2 expression, and promoting the proliferation of PASMCs.