Abstract: Objective :To explore the level of CIK cells in peripheral blood of patients with ad-vanced lung cancer and to analyze its clinical significance. Methods :Flow cytometry was used to de-tect CIK cells in peripheral blood of 57 patients with advanced lung cancer and 27 normal donors. CIKcells in peripheral blood of 35 patients who received 3 cycles of chemotherapy were also measured twoweeks after chemotherapy. Results :The level of CIK cells in peripheral blood of patients with lungcancer was significantly higher than that found in normal donors. There was no relationship between thelevel of CIK cells and pathology, but the CIK cell level increased with TNM stage.The level of CIKcells decreased after chemotherapy. Conclusion :There is an elevated level of CIK cells in patientswith advanced lung cancer. Increased levels of CIK cells might have significant anti-tumor effect.There is no relationship between the level of CIK cells and pathological types, but the CIK cell level isaffected by TNM stage and therapy. CIK cell level may be a useful indicator in the assessment of ad-vanced lung cancer.