Epidermal Growth Factor (EGF) is a core member of the EGF superfamily of peptide growth factors, a conserved family with EGF-like structural domains. As a potent mitogen, EGF exerts pivotal biological functions by binding to its transmembrane receptor EGFR (ErbB1) and triggering downstream signaling cascades like Ras-MAPK and PI3K-Akt. It robustly promotes the proliferation of epithelial, mesenchymal and neural cells, accelerates cell migration and tissue regeneration, and modulates cell differentiation. Notably, EGF does not induce apoptosis; instead, it suppresses apoptotic pathways to enhance cell survival, playing indispensable roles in embryonic development, wound healing and normal tissue homeostasis.To test the effect of EGF on cell proliferation of Balb/3T3, Balb/3T3 cells were seeded into triplicate wells of 96-well plates at a density of 4, 000 cells/well and allowed to attach overnight, then the medium was replaced with various concentrations of recombinant human EGF with serum-free standard DMEM. After incubated for 72h, cells were observed by inverted microscope and cell proliferation was measured by Cell Counting Kit-8 (CCK-8). Briefly, 10 µl of CCK-8 solution was added to each well of the plate，then measure the absorbance at 450 nm using a microplate reader after incubating the plate for 1-4 hours at 37 °C. The dose-effect curve of EGF was shown in Figure 1. It was obvious that EGF significantly promoted cell proliferation of Balb/3T3 cells .The ED50 is 0.151 ng/ml.