Promoting the antitumor effects of cell‐based immunotherapy for clinical application remains a difficult challenge. Nocardia rubra cell‐wall skeleton (N‐CWS) is an immunotherapeutic agent for cancers that have been proven to possess the ability to activate immune response without showing toxicity. However, its effects on immune cells that are derived from tumor patients and cultured in vitro remain unclear. As expected, N‐CWS can enhance the proliferation and viability of cytokine‐induced killer (CIK) cells, dendritic cells (DCs), and natural killer (NK) cells.