Recently, there has been a growing research interest in the application of immunotherapy for cancer treatment. Various approaches have been developed, and one of these methods involves utilizing Natural Killer (NK) cells of the immune system to specifically target cancer cells. Research on this method necessitates the mass and stable production of NK cells through culturing. For NK cell culture, Fetal Bovine Serum (FBS) is widely used in the industry at concentrations ranging from 10% to 20%. In an effort to explore a more efficient culturing technique, this study aims to investigate the effect of 1% FBS on cell viability of NK cells in cell culture. Because NK cells are usually defined by cell surface molecules, the efficacy of using a lower FBS concentration was quantitatively measured using Fluorescence-Activated Cell Sorting (FACS). The cell counts of cells cultured in 1% FBS was compared to those of cells cultured in 10% FBS. The results showed that no significant difference was found between cell count of cells cultured in 1% and 10% FBS. Thus, 1% FBS concentration culturing method was not found to be inferior. Further research is needed on the effect of replicating cancer microenvironment on NK cell viability.