Interleukin 15 (IL15) is a widely expressed cytokine that is structurally and functionally related to IL2, which plays an important role in many immunological diseases. IL15 also regulates T and natural killer (NK) cell activation and proliferation. The activity of recombinant pig IL15 was measured in a cell proliferation assay using MO7e human megakaryocytic leukemic cells. MO7e cells were seeded into triplicate wells of 96-well plates at a density of 30,000 cells/well in RPMI-1640 with the addition of various concentrations of rpIL15. 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 1-4 hours at 37 °C. Cell proliferation of MO7e cells after incubation with rpIL15 for 72h observed by inverted microscope was shown in Figure 1. The dose-effect curve of rpIL15 was shown in Figure 2. It was obvious that rpIL15 significantly promoted cell proliferation of MO7e cells .The EC50 for this effect is typically 0.55 ug/ml.