Recently, an anticontractile effect of periadventitial fat was discovered. The hypothesis was tested that periadventitial fat affects the contractility of rat skeletal muscle small arteries by acting on smooth muscle Kv channels using wire myography. In arteries surrounded by periadventitial fat, the concentration response relationship for serotonin-induced contractions is located at higher serotonin concentrations compared to arteries without fat (pD₂: 6.82±1.03 and 7.39±0.11 in the presence and absence of fat). Similar differences are observed for the vasoconstrictor U46619, but not for phenylephrine and the vasodilator NO. Removal of the endothelium does not affect the difference of the concentration response relationships for serotonin in vessels with and without fat. However, this difference is abolished when vessels are constricted by KCl suggesting the involvement of potassium channels. Indeed, the concentration response relationships for serotonin do overlap in the presence of 2 mM 4-AP, a specific inhibitor of Kv channels, but not in the presence of inhibitors of BK and ATP-sensitive K channels and Kv2 channels. Thus, the data show that periadventitial fat reduces the contractility of rat skeletal muscle small arteries. This effect seems to be mediated by 4-AP-sensitive potassium channels in smooth muscle cells.