Aim 15‐Lipoxygenase (15‐LO) is an important factor in the pathogenesis of pulmonary artery hypertension (PAH). However, the role of 15‐LO in the adventitia of the pulmonary arterial wall is unclear. The aim of this study was to explore the role of 15‐LO in the modulation of pulmonary adventitial fibroblast (PAF) dynamics. Methods Rats were exposed to normoxic or hypoxic (fraction of inspired O2 = 0.12) treatments for 7 days. PAF proliferation and cell cycle alterations were measured by MTT assay, cell immunofluorescence, flow cytometry and Western blot analysis. The 15‐LO promoter was analysed by luciferase reporter and ChIP assays. Results Our results showed that hypoxia induced 15‐LO expression in PAFs both in vivo and in vitro. In addition, hypoxia stimulated JNK phosphorylation in PAFs. Blocking 15‐LO or JNK suppressed 15‐LO‐induced PAF proliferation and cell cycle alterations. The inhibition of p27kipl by gene silencing attenuated 15‐LO‐induced PAF proliferation and cell cycle alterations. Furthermore, JNK inhibition or Elk‐1 knockdown suppressed hypoxia‐induced 15‐LO expression in PAFs. Luciferase reporter and ChIP assays revealed that the 15‐LO promoter contains Elk‐1‐binding sites and also that Elk‐1 increased the hypoxia‐induced activity of the 15‐LO promoter. Conclusion These results suggest that hypoxia promotes changes in the cellular dynamics of PAFs by inducing 15‐LO expression, which leads to vascular adventitial remodelling. The modulation of p27kipl expression by 15‐LO enhances PAF proliferation and cell cycle alterations. Furthermore, the JNK‐dependent increase in Elk‐1 signalling is required for hypoxia‐induced 15‐LO expression in PAFs.