The aim of the present study was to examine the potential antitumor action of IFN-λ1 in human gastric carcinoma cell lines and the possible interaction between IFN-λ1 and human gastric carcinoma cells. Gastric carcinoma HGC-27 and SGC-7901 cells were treated with IFN-λ1 (0, 10, 100, 1000 ng/ml) for 48 h. Cytotoxicity was examined using an MTT method. Cell cycle distribution was examined using propidium iodide staining. Apoptosis was examined using the Annexin V-FITC/PI apoptosis kit. By using flow cytometry and JC-1 probe, the mitochondrial membrane potential of cells following treatment with IFN-λ1 was also examined. Expression levels of representative apoptosis‑related proteins were evaluated by western blot analysis. IFN-λ1 inhibited the proliferation of gastric carcinoma cells in a concentration‑dependent manner. IFN-λ1 increased the accumulation of cells in the sub-G0 phase and arrested the cells in the G1 phase. Exposure to IFN‑λ1 decreased the mitochondrial membrane potential and increased apoptosis. Moreover, IFN‑λ1 exposure upregulated the expression of p21, p27 and Bax, downregulated the expression of Bcl‑2, increased the release of cytochrome c and apoptosis-inducing factor (AIF) and activated caspase-3 and caspase-9. In conclusion, IFN-λ1 inhibits the proliferation of gastric carcinoma cells by arresting the cells in the G1 phase and by inducing mitochondrial‑mediated apoptosis.