Background: Growing researches have focused on obesity as an useful prognostic factor for pan-cancer patients with immmnotherapy. The role of body-mass index (BMI) in predicting response to ICIs is not consistent in different tumors. This meta-analysis was conducted to evaluate the relationship between BMI and outcome in patients with advanced non-small cell lung cancer treated with immune checkpoint inhibitors, which is not clear as studies have demonstrated inconsistent results and significant interpretation biases. Methods: We searched PubMed and Embase, for relevant studies published up to December 2022. Title/abstract screening, full-text review, data extraction, and quality assessment were performed independently. Results: The correlation between BMI and prognosis in patients with advanced non-small cell lung cancer treated with ICIs was compared in ten trials encompassing 5000 individuals with the disease. The findings showedthat immunotherapy was significantly more effective for non-small cell lung cancer patients with a higher BMI compared to those with a lower BMI (OS: HR: 0.832, 95% CI: 0.725-0.955, p = 0.009; PFS: HR: 0.860, 95% CI: 0.771-0.960, p = 0.007). While，in the investigation of the obese group, no statistically significant differences were found. Conclusions: In patients with advanced non-small cell lung cancer treated with ICIs, appropriate higher BMI was significantly linked to better outcomes. However, discrepant findings from different cutoff subgroup analyses urgently call for further analysis.