Fibulin?2 (FBLN2) is the second largest member of the seven-member fibulin family of extracellular membrane (ECM) glycoproteins. The protein is known to form disulfide-linked homodimers, but it can also be secreted as an oligomer. Fibulin?2 is considered a multifunctional binding protein due to its association with numerous ECM components, but its specific interactions have yet to be determined. Fibulin?2 is localized at the interface between microfibrils and the elastin core and its known interactions include nidogen-1, perlecan, laminin, aggrecan, endostatins, versican, collagen, and tropoelastin. It is down-regulated in numerous forms of cancer including breast, colorectal, lung, esophageal, and squamous cell carcinoma, but over-expression has been shown with solid tumors. To test the effect of FBLN2 on cell apoptosis, A549 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 rat FBLN2 diluted with 5% serum 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 the absorbance at 450 nm was measured using a microplate reader after incubating the plate for 1h at 37℃. Proliferation of A549 cells after incubation with FBLN2 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 rat FBLN2 for 72h. The result was shown in Figure 2. It was obvious that FBLN2 significantly inhibit cell viability of A549 cells. The ED50 is 0.97 μg/mL.