S100A11 is a member of the S100 calcium-binding protein family ,it contains two EF-hand calcium-binding motifs and shares 82% amino acid sequence identity with mouse and rat S100A11 . S100 proteins are localized in the cytoplasm and nucleus of a wide range of cells, and involved in the regulation of a number of cellular processes such as cell cycle progression and differentiation. This protein may function in motility, invasion, and tubulin polymerization. Chromosomal rearrangements and altered expression of this gene have been implicated in tumor metastasis .When extracellular calcium concentrations elevate ,S100A11 will associate with S100B as well as Annexins A1, A2, and A6. S100A11-Annexin A2 complexes are recruited to sites of plasma membrane damage where they facilitate membrane repair in migrating cancer cells. Thus a binding ELISA assay was conducted to detect the interaction of S100A11 and Annexin A2. Briefly, recombinant human S100A11 were diluted serially in PBS, with 0.01%BSA (pH 7.4). Duplicate samples of 100ul were then transferred to Annexin A2-coated microtiter wells and incubated for 2h at 37°C. Wells were washed with PBST and incubated for 1 h with anti-S100A11 mAb, 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°C. Finally, add 50µL stop solution to the wells and read at 450nm immediately. The binding activity of of S100A11 and Annexin A2 was shown in Figure 1, and this effect was in a dose dependent manner.