The tuber of amorphophallus konjac (TuAK) is an antitumor herb used in traditional Chinese medicine. The present study investigated the inhibitory effect of TuAK against gastric cancer and the underlying mechanisms associated with two programmed cell death pathways, apoptosis and autophagy. TuAK was extracted by organic solvents including ethanol and ligarine. The extract of TuAK, shortened as TuAKe, significantly inhibited the growth of cultured gastric cancer cell lines SGC-7901 and AGS, with IC50 of 35-45 µg/ml. TuAKe could increase cell apoptosis and induce cell cycle arrest. For the apoptosis-associated proteins, expressions of survivin and Bcl-2 were decreased by treatment of TuAKe, and the expression of Bax and caspase-9 was increased. Furthermore, TuAKe could promote autophagy, and the antitumor efficacy of TuAKe was significantly hampered by targeted suppression of autophagy, suggesting that autophagy contributed to TuAKe-induced cell death. Furthermore, patients with gastric cancer who received TuAK-based medicinal decoction achieved improved scores in assessment of life quality compared with those without TuAK treatment. This study demonstrated the antitumor activity of TuAKe against gastric cancer, and is the first report to show that the underlying mechanism is associated with induction of autophagy. Our data provided support of the clinical use of amorphophallus konjac-based medication in combination with classical chemotherapy to achieve optimized outcome for gastric cancer.