FGF13 (Fibroblast growth factor 13) is a member of the fibroblast growth factor (FGF) family. FGF family members possess broad mitogenic and cell survival activities, and are involved in a variety of biological processes, including embryonic development, cell growth, morphogenesis, tissue repair, tumor growth, and invasion. A proliferation assay was conducted to detect the bioactivity of recombinant rat FGF13 using 3T3 cells. Briefly,?3T3 cells were seeded into triplicate wells of 96-well plates at a density of 2,000 cells/well and allowed to attach overnight, then the medium was replaced with serum-free standard DMEM?prior to the addition of various concentrations of FGF13. After incubated for 48h,?cells were observed by inverted microscope and cell proliferation was measured by Cell Counting Kit-8 (CCK-8). Briefly, 10μL of CCK-8 solution was added to each well of the plate, then the absorbance at 450nm was measured using a microplate reader after incubating the plate for 1-4 hours at 37℃. Proliferation of 3T3 cells after incubation with FGF13 for 48h observed by inverted microscope was shown in Figure 1. Cell viability was assessed by CCK-8 (Cell Counting Kit-8 ) assay after incubation with recombinant FGF13 for 48h. The result was shown in Figure 2. It was obvious that FGF13 significantly increased cell viability of 3T3 cells.