There is mounting evidence that garlic extracts possess significant anticancer actions. However, no studies have been reported on the effects of aged black garlic extracts (ABGE) on gastric cancer in vitro or in vivo. To examine the potential action of ABGE against gastric cancer, the present study evaluated its effect on the inhibition of cell proliferation and induction of apoptosis in SGC-7901 human gastric cancer cells. Additionally, we performed an in vivo study by inoculating the murine foregastric carcinoma cell line in Kunming mice and treating them with various doses of ABGE (0, 200, 400 and 800 mg/kg, intraperitoneally) for 2 weeks. Dose-dependent apoptosis was detected in ABGE-treated cells in in vitro studies. In tumor-bearing mice, significant antitumor effects of ABGE were observed, such as growth inhibition of inoculated tumors. Further investigation of serum superoxide dismutases, glutathione peroxidase, interleukin-2 and the increased indices of spleen and thymus indicated that the anticancer action of ABGE may be partly due to its antioxidant and immunomodulative effects.