Britanin was explored for the antitumour effect on gastric cancer, which is a sesquiterpene lactone (SL) extracted from Inula japonica.In the present study, cell viability assays were performed to evaluate the antiproliferation effect of Britanin on gastric cancer cells. Tumour development in BGC-823 cell-bearing nude mice was monitored in real-time after Britanin treatment via a bioluminescent imaging method. Western blotting analysis and enzyme-linked immunosorbent assays detected proteins associated with the nuclear factor (NF)-κB signalling pathway.Britanin can suppress the proliferation of gastric cancer cells in vitro and the growth of tumours in vivo. In the treatment group, decreased levels of p65 and phosphorylated (p)-p65 were observed. This indicated that NF-κB plays an important role in the antitumour effect of Britanin. Furthermore, considering the additional role of NF-κB in the immune system, the levels of the downstream molecules interleukin (IL)-2 and the cytokine IL-10 were subsequently determined in vivo. An increase in the IL-2 level and a decrease in the IL-10 level indicated that Britanin elicited an enhanced immune response.Britanin may be a promising candidate for gastric cancer chemotherapy, and its anticancer effect likely depends on an NF-κB-mediated immune response.