Proliferation of adventitial fibroblasts of small intrapulmonary arteries (FBPA) has been disclosed as an early event in the development of pulmonary hypertension and cor pulmonale in response to hypoxia. We investigated the role of hypoxia‐inducible transcription factors (HIF) in human FBPA exposed to hypoxia. Primary cultures of FBPA displayed a strong mitogenic response to 24 h hypoxia, whereas the rate of apoptosis was significantly suppressed. In addition, the migration of FBPA was strongly increased under hypoxic conditions but not the expression of α‐smooth muscle actin. Hypoxia induced a marked up‐regulation (protein level) of both HIF‐1α and HIF2α, alongside with nuclear translocation of these transcription factors. Specific inhibition of either HIF‐1α or HIF‐2α was achieved by RNA interference technology, as proven by HIF‐1α and HIF‐2α mRNA and protein analysis and expression analysis of HIF downstream target genes. With the use of this approach, the hypoxia‐induced proliferative response of the FBPA was found to be solely HIF‐2α dependent, whereas the migratory response was significantly reduced by both HIF‐1α and HIF‐2α interference. In conclusion, HIF up‐regulation is essential for hypoxic cellular responses in human pulmonary artery adventitial fibroblasts such as proliferation and migration, mimicking the pulmonary hypertensive phenotype in vivo. Differential HIF subtype dependency was noted, with HIF‐2α playing a predominant role, which may offer future intervention strategies.