Ganoderic acid Me (GA-Me) is a lanostane triterpenoid purified from Ganoderma lucidum mycelia, one of the most widely used herbs for cancer treatment and prevention in east Asia. In the present study, it was demonstrated that GA-Me could inhibit both tumor growth and lung metastasis of Lewis lung carcinoma in C57BL/6 mice. Compared with the control group, Natural Killer (NK) cells activity was significantly enhanced by intraperitoneal administration of GA-Me (28 mg/kg). Results of ELISA assay and RT-PCR showed that the expressions of Interleukin-2 (IL-2) and Interferon-gamma (IFN-gamma) were also increased (p<0.05). Additionally, the expression of Nuclear Factor-kappaB (NF-kappaB) was up-regulated after the treatment of GA-Me, which might be involved in the production of IL-2. In conclusion, the findings of this study implied that GA-Me could effectively inhibit tumor growth and lung metastasis through increasing immune function.