Recombinant human granulocyte‐colony stimulating factor (rhG‐CSF) is the most common hematopoietic growth factor used for chemotherapy‐induced neutropenia or mobilization of stem cells. Natural killer (NK) cells are critical for host defense against infected cells and tumors. However, the cellular and molecular events of NK cells responding to rhG‐CSF remain unclear. Toward this end, we treated human NK cells with rhG‐CSF and assessed their cytotoxic function as well as proteomic characteristics. Unlike the other tested hematopoietic cytokines, rhG‐CSF decreased NK cell‐mediated cytotoxicity without affecting the viability of NK cells. The rhG‐CSF also reduced the production of nitric oxide and expression of inducible nitric oxide synthase in recombinant human interleukin (rhIL)‐2‐activated NK cells. By using cytokine array, rhG‐CSF reduced secretion of growth‐related oncogene‐α from NK cells. Intriguingly, rhG‐CSF did not affect production of various inflammatory cytokines [MCP‐1, IL‐6, tumor necrosis factor‐α (TNF‐α), granulocyte‐macrophage colony‐stimulating factor (GM‐CSF) and IL‐8], which are markedly stimulated by rhGM‐CSF. Proteomic analysis of rhG‐CSF‐ and rhGM‐CSF‐treated NK cells uncovered unique proteins possibly involving rhG‐CSF effect. These proteins were classified into six groups as follows: glycolysis, apoptosis, cytotoxicity, inflammation, antigen processing and presentation, and the others. We conclude that rhG‐CSF may impair NK‐mediated cytotoxicity accompanied by alterations in protein expression profile distinct from that of rhGM‐CSF.