Insulin Like Growth Factor Binding Protein 1 (IGFBP1) is a member of the IGFBP family that binds to insulin-like growth factors (IGFs) with high affinity. IGFBP1 plays a crucial role in regulating the biological activities of IGFs, which are important for growth and development. IGFBP1 is primarily produced in the liver and is also secreted by various other tissues, including the decidua of the uterus during pregnancy. Its levels in the bloodstream are influenced by factors such as nutritional status, insulin levels, and growth hormone. To detect the activity of recombinant GFBP1,a functional ELISA assay was conducted to detect the interaction of recombinant rat IGFBP1 and recombinant human Insulin Like Growth Factor 1 (IGF1). Briefly, IGFBP1 was diluted serially in PBS with 0.01% BSA (pH 7.4). Duplicate samples of 100 μl were then transferred to IGF1-coated microtiter wells and incubated for 1h at 37℃. Wells were washed with PBST and incubated for 1h with anti-IGFBP1 pAb, then aspirated and washed 3 times. After incubation with HRP labelled secondary antibody for 1h at 37℃, 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 450/630nm immediately. The binding activity of recombinant rat IGFBP1 and recombinant human IGF1 was shown in Figure 1, the EC50 for this effect is 0.222ug/mL.