Plasminogen Activator Inhibitor 1 (PAI1) is a member of the Serpin superfamily of serine protease inhibitors, Serpin E1/PAI 1 is the principal inhibitor of urokinase type plasminogen activator (uPA) and tissue type PA. As important regulators of extracellular matrix remodeling, uPA and PAI 1 play a major role in many processes such as angiogenesis, tumor invasion and obesity. Besides, Vitronectin (VTN) has been identified as an interactor of PAI1, thus a binding ELISA assay was conducted to detect the interaction of recombinant human PAI1 and recombinant human VTN. Briefly, PAI1 were diluted serially in PBS, with 0.01% BSA (pH 7.4). Duplicate samples of 100 µl were then transferred to VTN-coated microtiter wells and incubated for 2h at 37℃. Wells were washed with PBST and incubated for 1h with anti-PAI1 pAb, then aspirated and washed 3 times. After incubation with HRP labelled secondary antibody, wells were aspirated and washed 3 times. With the addition of substrate solution, wells were incubated 15-25 minutes at 37℃. Finally, add 50µL stop solution to the wells and read at 450nm immediately. The binding activity of PAI1 and VTN was shown in Figure 1, and this effect was in a dose dependent manner, the EC50 was approximately 4.47 ug/mL.