We examined the effects of an Antrodia cinnamomea ethanol extract (ACEE) on lung cancer cells in vitro and tumor growth in vivo. ACEE produced dose-dependent cytotoxic effects and induced apoptosis in Lewis lung carcinoma (LLC) cells. ACEE treatment increased expression of p53 and Bax, as well as cleavage of caspase-3 and PARP, while reducing expression of survivin and Bcl-2. ACEE also reduced the levels of JAK2 and phosphorylated STAT3 in LLC cells. In a murine allograft tumor model, oral administration of ACEE significantly inhibited LLC tumor growth and metastasis without affecting serum biological parameters or body weight. ACEE increased cleavage of caspase-3 in murine tumors, while decreasing STAT3 phosphorylation. In addition, ACEE reduced the growth of human tumor xenografts in nude mice. Our findings therefore indicate that ACEE inhibits lung tumor growth and metastasis by inducing apoptosis and by inhibiting the STAT3 signaling pathway in cancer cells.