Abstract Background Researchers are particularly interested in the plants of the genus Inula because of their potent medicinal applications. Britannin, a sesquiterpene lactone isolated from Inula aucheriana DC., exerts potent cytotoxicity towards various human cancers. In this study, we examined the involvement of the PPARγ pathway in the antitumor effect of Britannin against gastric cancer cells. Methods and Results Cytotoxic activity of Britannin was evaluated by MTT assay, followed by Annexin V-FITC/PI staining and caspase-3 activity assay. The expression levels of Nuclear factor kappa B (NF-κB), Inhibitor of nuclear factor kappa B (IκBα), and Peroxisome proliferator-activated receptor γ (PPARγ) were determined by western blotting. Quantitative RT-PCR was used to measure the effect of Britannin on the expression of NF-κB target genes. Our results showed that Britannin inhibited gastric cancer cell growth by inducing apoptotic death. The mRNA and protein levels of PPARγ were significantly increased following treatment with Britannin. The involvement of PPARγ was more confirmed using GW9662, a PPARγ inhibitor. Suppression of NF-κB was also demonstrated by western blot analysis. Down-regulation of Cyclooxygenase-2 (COX-2), Matrix Metalloproteinase 9 (MMP-9), Twist Family BHLH Transcription Factor 1 (TWIST-1), and B-cell lymphoma 2 (Bcl-2) and upregulation of Bcl-2-Associated x (Bax) were also observed in gastric cancer cells treated with Britannin. Conclusions These results imply that activation of the PPARγ signaling pathway through suppression of NF-κB underlies the anti-cancer properties of Britannin in gastric cancer. Therefore, Britannin could be considered for further investigations to explore novel potent anti-cancer drugs.