Perivascular adipose tissue (PVAT) is situated outside of almost every blood vessel. Recent studies showed that PVAT provides mechanical support for blood vessels and secretes vasoactive adipokines that could regulate vascular tone. However, most of the studies evaluating PVAT effects on vascular tone have been performed with vessels derived from animals. Therefore, we aimed to investigate the role of PVAT surrounding human coronary bypass graft vessels such as saphenous vein (SV). Human SV preparations were set up in an organ bath in the presence or absence of their PVAT. The presence of PVAT significantly attenuated the contractile response to prostaglandin F-2 alpha (PGF(2 alpha)). However, potassium chloride (KCI)-induced concentration-response curve wasn't modified in PVAT-intact SV preparations. On the other hand, endothelium-dependent relaxation induced by acetylcholine (ACh) or endothelium-independent relaxation induced by sodium nitroprusside (SNP) were similar between SV with PVAT versus SV without PVAT preparations. Sensitivity of the SV to contractile agonists (KCI, PGF(2 alpha)) or relaxant agonists (SNP, ACh) were not modified in the presence of PVAT. These results suggest that PVAT could decrease PGF(2 alpha)-induced contractile tone via endothelium-independent mechanisms in SV. Retaining PVAT in SV preparations during bypass graft surgery could prevent graft vasospasm possibly via PVAT derived relaxant factor(s).