Smoking　is　an　independent　risk　factor　for　the　cardiovascular　diseases.　Nicotine,　a　major　component　of　tobacco,　is　responsible　for　the　impaired　endothelial-dependent　vasorelaxation　in　smokers.　Procyanidin　B2　(PCB2),　a　natural　flavonoid,　has　been　reported　to　possess　several　potential　beneficial　effects　on　the　cardiovascular　system.　However,　whether　PCB2　prevents　nicotine-induced　endothelial　dysfunction　remains　unknown.　In　this　study,　we　demonstrated　that　PCB2　improved　nicotine-impaired　endothelium-dependent　vasorelaxation　in　mouse　thoracic　aortas.　Mechanistically,　PCB2　increased　the　expression　levels　of　dihydrofolate　reductase　(DHFR)　and　GTP　cyclohydrolase　1　(GCH1),　two　important　enzymes　in　the　synthesis　of　tetrahydrobiopterin　(BH4),　in　mouse　aortas　and　cultured　ECs.　GSK0660,　a　selective　antagonist　of　peroxisome　proliferator-activated　receptor　δ　(PPARδ),　abolished　the　PCB2-induced　effects　on　BH4　synthesis,　nitric　oxide　(NO)　production　and　vasodilation.　Collectively,　we　demonstrated　that　PCB2　mitigates　nicotine-induced　endothelial　dysfunction　through　a　PPARδ-BH4　dependent　manner,　thereby　suggesting　a　novel　role　of　PCB2　in　preventing　vascular　dysfunction　caused　by　nicotine　exposure.　©　2022　The　Author(s)