Objective:To investigate the variation of immunophenotype and cytotoxic activity of autologous cytokine-induced killer (CIK) cells in patients with malignant tumors, and explore the best time of adoptive immunotherapy infusion of CIK cells. Methods:Peripheral blood mononuclear cells (PBMC) in 40 patients with malignant tumors were collected and cultivated into CIK cells in vitro by biotechnology under induction of several kinds of cytokines including interferon γ (IFN-γ), recombinant human interleukin 1α (rhIL-1α), CD3 monoclonal antibody (CD3McAb) and recombinant human interleukin 2 (rhIL-2). Immunophenotypes were dynamically monitored by lfow cytometry (FCM), and cytotoxic activity was analyzed by methyl thiazolyl tetrazolium (MTT) method. Results:After induction and expansion at different time, CD3+, CD3+CD8+and CD3+CD56+in mononuclear cells (MNC) had an up-regulated tendency. CD3+CD4+reached the peak on day 7, and then decreased slowly;CD25 reached the peak in earlier period of cultivation (3-7 days), and decreased slowly in 7-14 days, and then decreased rapidly in 14-21 days. Human leukocyte antigen DR (HLA-DR) was on the rise in 0-14 days, and decreased rapidly after reaching the peak on day 14. The cytotoxic activity of mature CIK cells was signiifcantly higher than that of non-activated PBMC, and the difference was statistically signiifcant (P