Aims: To investigate changes in cellular immune function of patients with lung cancer before and after cytokine-induced killer (CIK) cell therapy and to identify variation effects on overall survival (OS) and progression-free survival (PFS). Materials and Methods:A total of 943 lung cancer patients with immune dysfunction were recruited from January 2002 to January 2010, 532 being allocated to conventional therapy and 411 to CIK therapy after a standard treatment according to the NCCN Clinical Practice Guidelines. All the patients were investigated for cellular immune function before and after therapy every three months. and clinical prognostic outcomes were analyzed. Results: After six courses of treatment, immune function was much improved in patients receiving CIK cells therapy as compared to controls. The percentages of recurrence and/or metastases for patients undergoing CIK cell therapy was 56.2% and 49.1% respectively but 78.6% and 70.3% among controls (p<0.001). The median OS times for CIK cell therapy and control groups were 48 and 36 months respectively. The OS rates at 12, 36, 60, 84 months in CIK treated patients were 97.8%, 66.9%, 27.7%, and 4.1% while they were 92.3%, 44.5%, 9.2%, and 1.5% in controls. OS and PFS were significantly different by log rank test between the two groups and across the three immune improvement classes. Conclusions: The immune function of lung cancer patients was improved by CIK cell therapy, associated with an increase in the OS rate and extension of the time to recurrence and/or metastasis.