Transforming growth factor beta 1 or TGF-β1 is a polypeptide member of the transforming growth factor beta superfamily of cytokines. It is a secreted protein that performs many cellular functions, including the control of cell growth, cell proliferation, cell differentiation, and apoptosis. To test the effect of TGF-β1 on cell apoptosis, HepG2 cells were seeded into 96-well plates including various concentrations of recombinant mouse TGF-β1. 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 the absorbance at 450 nm was measured using a microplate reader after incubating the plate for 1-2 hours at 37 ℃. Proliferation of HepG2 cells after incubation with TGF-β1 for 72h 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 mouse TGF-β1 for 72h. The result was shown in Figure 2. It was obvious that TGF-β1 significantly inhibit cell viability of HepG2 cells, the ED50 is 0.1 μg/ml.