This study investigates the role of lactylated apolipoprotein C-II (APOC2) in lung cancer and its impact on immunotherapy resistance. Global lactylome profiling and metabolomic analyses of non-small cell lung cancer (NSCLC) samples revealed that intracellular lactate promotes extracellular lipolysis through lactyl-APOC2. Mechanistically, lactate enhances APOC2 lactylation at lysine 70 (K70), stabilizing it and leading to the release of free fatty acids (FFAs) and regulatory T cell accumulation, which contributes to immunotherapy resistance and metastasis. The anti-APOC2K70-lac antibody, which sensitizes anti-PD-1 therapy in vivo, is developed. These findings highlight the potential of targeting lactyl-APOC2-K70 as a new combination therapy to enhance immunotherapeutic responses in NSCLC.This study investigates the role of lactylated apolipoprotein C-II (APOC2) in lung cancer and its impact on immunotherapy resistance. Global lactylome profiling and metabolomic analyses of non-small cell lung cancer (NSCLC) samples revealed that intracellular lactate promotes extracellular lipolysis through lactyl-APOC2. Mechanistically, lactate enhances APOC2 lactylation at lysine 70 (K70), stabilizing it and leading to the release of free fatty acids (FFAs) and regulatory T cell accumulation, which contributes to immunotherapy resistance and metastasis. The anti-APOC2K70-lac antibody, which sensitizes anti-PD-1 therapy in vivo, is developed. These findings highlight the potential of targeting lactyl-APOC2-K70 as a new combination therapy to enhance immunotherapeutic responses in NSCLC.