Extracellular Signal Regulated Kinase 2 (ERK2) is a 42-kDa protein serine/threonine kinase that is a member of the MAP kinase family. ERK2 is ubiquitously distributed in tissues with the highest expression in heart, brain, and spinal cord. Depending on the cellular context, the MAPK/ERK cascade mediates diverse biological functions such as cell growth, adhesion, survival and differentiation through the regulation of transcription, translation, cytoskeletal rearrangements. The MAPK/ERK cascade also plays a role in initiation and regulation of meiosis, mitosis, and postmitotic functions in differentiated cells by phosphorylating a number of transcription factors. It is reported that ERK2 can interact with STAT3 and treatment of cells with a MEK-ERK inhibitor blocks STAT3 S727 phosphorylation in response to IL-2. Thus a functional ELISA assay was conducted to detect the interaction of recombinant human ERK2 and recombinant human STAT3. Briefly, ERK2 was diluted serially in PBS with 0.01% BSA (pH 7.4). Duplicate samples of 100 μl were then transferred to STAT3-coated microtiter wells and incubated for 1h at 37℃. Wells were washed with PBST and incubated for 1h with anti-ERK2 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 human ERK2 and recombinant human STAT3 was shown in Figure 1, the EC50?for this effect is 1.06 ug/mL.