This study investigates the sensing properties and mechanisms of LaF3-Co3O4 nanorods for low-concentration methanol detection. Methanol is a characteristic gas that can distinguish between healthy individuals and lung cancer (LC) lesions in exhaled breath, with concentrations typically below one part per million (1×10−6). The research focuses on enhancing the gas-sensing performance of metal oxide semiconductor (MOS) materials using a second-phase composite method. LaF3-Co3O4 nanorods were synthesized via a hydrothermal method, and 5 at% LaF3-Co3O4 nanorods exhibited excellent methanol detection performance, including a wide linear detection range (0.2×10−6~5×10−6), a response value exceeding 4.0 for 1×10−6 methanol at 275 °C and 75% relative humidity (RH), long-term stability, and excellent selectivity. The enhanced performance is attributed to the special spinel structure of Co3O4, the high ionic migration of F− in LaF3, the larger specific surface area of the nanorods, and the generated crystal defects. This work provides a novel approach to preparing MOS composite materials for low-concentration methanol gas detection, which has significant potential for early LC diagnosis and treatment.This study investigates the sensing properties and mechanisms of LaF3-Co3O4 nanorods for low-concentration methanol detection. Methanol is a characteristic gas that can distinguish between healthy individuals and lung cancer (LC) lesions in exhaled breath, with concentrations typically below one part per million (1×10−6). The research focuses on enhancing the gas-sensing performance of metal oxide semiconductor (MOS) materials using a second-phase composite method. LaF3-Co3O4 nanorods were synthesized via a hydrothermal method, and 5 at% LaF3-Co3O4 nanorods exhibited excellent methanol detection performance, including a wide linear detection range (0.2×10−6~5×10−6), a response value exceeding 4.0 for 1×10−6 methanol at 275 °C and 75% relative humidity (RH), long-term stability, and excellent selectivity. The enhanced performance is attributed to the special spinel structure of Co3O4, the high ionic migration of F− in LaF3, the larger specific surface area of the nanorods, and the generated crystal defects. This work provides a novel approach to preparing MOS composite materials for low-concentration methanol gas detection, which has significant potential for early LC diagnosis and treatment.