Carcinoembryonic antigen (CEA), as one of the common tumor markers, is a human glycoprotein involved in cell adhesion and is expressed during human fetal development. Since the birth of human, CEA expression is largely inhibited, with only low levels in the plasma of healthy adults. Generally, CEA will overexpressed in many cancers, including gastric, breast, ovarian, lung, and pancreatic cancers, especially colorectal cancer. The lectin galactoside-binding soluble 3 binding protein (LGALS3BP) is also a secreted, which was first identified as cancer and metastasis associated protein. LGALS3BP has been identified as an interactor of CEA, thus a functional binding ELISA assay was conducted to detect the interaction of recombinant human CEA and recombinant human LGALS3BP. Briefly, biotin-linked CEA were diluted serially in PBS, with 0.01% BSA (pH 7.4). Duplicate samples of 100 ul were then transferred to LGALS3BP-coated microtiter wells and incubated for 1h at 37℃. Wells were washed with PBST 3 times and incubation with Streptavidin-HRP for 30min, then wells were aspirated and washed 5 times. With the addition of substrate solution, wells were incubated 15-25 minutes at 37℃. Finally, add 50 μl stop solution to the wells and read at 450 nm immediately. The binding activity of CEA and LGALS3BP was shown in Figure 1, and this effect was in a dose dependent manner.