Background <p>M2 macrophages play a pivotal role in promoting the growth and metastasis of lung cancer cells. Inhibiting M2 macrophage polarization represents an effective immunotherapeutic approach against tumors. Although (-)-Guaiol has been shown to exert potent inhibitory effects on M2 macrophage polarization, its underlying molecular mechanism remains unclear.</p> Objective <p>This study aimed to elucidate the effects of (-)-Guaiol on M2 macrophage polarization and to explore the potential molecular mechanisms involved.</p> Methods <p>Bone marrow-derived macrophages (BMDMs) from mice were polarized toward the M2 phenotype using IL-4 and M-CSF. Both ex vivo and in vivo experiments were performed to determine whether (-)-Guaiol suppresses M2 macrophage polarization through the PPAR-γ-related signaling pathway. PPAR-γ agonists and inhibitors were applied to confirm the involvement of PPAR-γ in the effects of (-)-Guaiol. A co-culture system of M2 macrophages and Lewis lung carcinoma (LLC) cells was established. Wound healing, Transwell invasion, and plate cloning experiments were performed to determine the effects of (-)-Guaiol on the metastasis and development of lung cancer cells.</p> Results <p>(-)-Guaiol markedly downregulated the expression of CD206, a characteristic surface marker of M2-polarized macrophages. It also significantly inhibited the proliferation, invasion, and metastatic potential of LLC cells co-cultured with M2 macrophages. Animal experiments revealed that (-)-Guaiol treatment significantly decreased the tumor volume and weight, as well as CD206 expression. Moreover, integrated in vitro and in vivo analyses revealed that (-)-Guaiol inhibited M2 macrophage polarization primarily by suppressing the PPAR-γ signaling pathway.</p> Conclusion <p>These findings demonstrate that (-)-Guaiol inhibits M2 macrophage differentiation via targeted suppression of the PPAR-γ-related signaling pathway, thereby reducing the proliferation, migration, and invasion of lung cancer cells.</p>