Abstract: Objective：To investigate the influence of comorbidities on tolerance to chemotherapy and patients’ survival in elderly patients with lung cancer. Methods：Fifty-one elderly patients (over 65 years old) with lung cancer were enrolled in this retrospective study, and their clinical characteristics were analyzed. Comorbidities were assessed using the Cumulative Illness Rating Scale for Geriatrics (CIRS-G). Chemotherapy-realted toxicity was graded using the common terminology criteria for adverse events (CTCAE v3.0). The correlation between comorbidities and chemotherapy-related serious adverse events and survival was analyzed. Results：The patients with severe comorbidities were more likely to have grade 3-4 lung infections and skin rashes (P=0.001), incomplete cycles (69% vs 32%, P=0.040), and changed chemotherapy regimens due to chemotherapy-related toxicities (69% vs 26%, P=0.021). The patients with high severity index had similar grade 3-4 chemotherapy-related toxicities as other patients, similar frequency of completing all cycles and chemotherapy regimens changing (P=0.827, P=0.174, and P=0.074). Age≥75 years old, stage Ⅲ-Ⅳ or chemotherapy regimens changing were independent predictors for progression-free survival in patients with lung cancer. There were no significant differences in progression-free survival when comparing patients with or without severe comorbidities (P=0.143) and patients with higher severity index versus those with the lower (P=0.868). But there was a tendency that the patients with severe comorbidity would have poorer progression-free survival. Conclusions：The patients with severe comorbidities had poorer tolerance to chemotherapy, were more likely to have incomplete cycles and changed chemotherapy regimens, and therefore might have poorer progression-free survival. The score of severe comorbidity was more sensitive than the severity index. However, these conclusions need to be further confirmed by trials with larger sample size .