PURPOSE: Programmed cell death-1 (PD-1)/programmed death-ligand 1 (PD-L1) inhibitors plus chemotherapy have become the standard first line of treatment in patients with advanced non-small-cell lung cancer (NSCLC). However, few studies have explicitly focused on the impact of weight loss on the efficacy of PD-1/PD-L1 inhibitors plus chemotherapy. Thus, we evaluated the clinical implications of weight loss on the survival outcomes in patients who received this treatment. METHODS: We conducted a retrospective review of medical records of patients with advanced NSCLC who were treated with PD-1/PD-L1 inhibitors plus chemotherapy from December 2018 to December 2020. Significant weight loss was defined as an unintentional weight loss of 5% or more over 6 months. We evaluated the progression-free survival (PFS) and overall survival (OS) of patients with or without weight loss. RESULTS: Among the 80 included patients, 37 (46%) had weight loss, and were associated with a lower objective response rate (30 vs 51%, P < 0.05), poorer PFS (2.3 vs 12.0 months, P < 0.05), and poorer OS (10.8 vs 23.9 months, P < 0.05) than those without weight loss. The Cox proportional-hazard ratios (95% confidence interval) of weight loss were 1.77 (1.01-3.10) for PFS and 2.90 (1.40-6.00) for OS, with adjustments for Eastern Cooperative Oncology Group performance status, PD-L1 tumour proportion score, histology, and central nervous system metastases. CONCLUSION: Pre-treatment weight loss may reduce treatment efficacy and shorten survival time in patients receiving PD-1/PD-L1 inhibitors plus chemotherapy. Early evaluation and intervention for weight loss might improve oncological outcomes in patients with advanced NSCLC.