ALX-0081 is a novel nano-antibody inhibiting von Willebrand factor (vWF). We evaluated whether direct inhibition of vWF by ALX-0081 improves endothelial function. Stable patients (pts, n = 55) with single vessel disease undergoing percutaneous coronary intervention (PCI) were randomized to ALX-0081 (n = 38) or placebo (n = 17). vWF inhibition was assessed by vWF antigen level (vWF:Ag) and activity by ristocetin test (vWF:RiCo). Endothelial function was assessed before (BL), 6 h and 24 h after PCI by: (a) endothelial peripheral arterial tonometry (Endoscore); (b) endothelial microparticles (EMPs) by flow cytometry. vWF:Ag and vWF:RiCo decreased within 1 h from ALX-0081. In the placebo group, no significant Endoscore changes occurred from BL to 24 h. In ALX-0081 group, Endoscore increased from BL to 24 h (p = 0.014). A decrease in EMPs was observed after ALX-0081 (p < 0.01), while no changes occurred in placebo pts. An inhibition of vWF with ALX-0081 significantly improves peripheral endothelial function.