Objective Diabetes mellitus is well known risk factors of several cancers including pancreatic, breast, and colorectal cancer. However, relationship between diabetes and lung cancer is still unclear. Recently, some studies reported diabetes is independently associated with mortality of lung cancer. The aim of this study is to determine the effect of diabetes on lung cancer survival. Methods We retrosepctively reviewed medical records of 2,164 patients co-existed diabetes and lung cancer at the time of diagnosing lung cancer who attended Chonnam National University Hwasun Hospital between 2005 and 2012. Results The overall survival of lung cancer between diabetic patient group (262 cases) and non-diabetic patient group (1,902 cases) is not different (P = 0.920). There is no significant difference between diabetic group and non-diabetic group in sub-group analysis though first-line therapy and cancer type (SCLC and NSCLC). Well controlled diabetes (HbA1c < 7%) cound not make difference on survival rate of lung cancer in diabetic patients (P = 0.19) Conclusion We had better avoid too strict blood sugar control in advanced lung cancer patients considering mean survival time and general condition. More prospective and bio-molecular study are needed to examine the effect of diabetes on cancer cell growth in lung cancer patients.