AIM: To reveal whether H2O2, a kind of platelet - derived growth factor (PDGF) signaling molecule, involved in the proliferation of phypoxic pulmonary arlmonary artery smooth muscle cells (PASMCs) and expression of transcription factor NF -?B. METHODS: bar confocal scanning microscopy,immunocytochemistry and Western blot analysis were used. RESULTS: PDGF (30 ng/mL) elevated the intracellular H2O2 in normoxic PASMCs, but decreased that of hypoxic PASMCs significantly. When 100?mol/L H2O2 was added, NF - ?B expression were inhib- ited markedly in hypokic PASMCs, while the same concentration H2O2 resulted in increase of NF - ?B expression in control cells. CONCLUSION: H2O2, a mediator molecule of PDGF signal transduction, act as an inhibitor in hy- poxic PASMCs which is qUiet different from that in normoxic PASMCs. It may effect on the expression of transcription factor NF -?B. NF - ?B induce various gene expression that involving in the proliferation of vascular smooth muscle cells. One mechanism by which PDGF - induced hypoxic PASMC proliferation might be through PDGF alleviating H2O2 inhibition.