Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) is a potent anti-tumor agent that triggers apoptosis in cells from multiple types of carcinoma but not in normal cells. However, diverse mechanisms are associated with insensitivity to TRAIL in various cancers. TRAIL efficacy may be enhanced by combining TRAIL with a sensitizer. In this study, vernodalol, a sesquiterpene lactone, sensitized diffuse large B-cell lymphoma (DLBCL) cells to TRAIL-induced apoptosis. Vernodalol increased the expression of death receptor (DR) 5, and silencing of DR5 with a small interfering RNA (siRNA) reduced the effect of vernodalol on TRAIL-mediated apoptosis. Additionally, vernodalol up-regulated the expression of CCAAT/enhancer-binding protein (C/EBP) homologous protein (CHOP), a transcription factor. Inhibition of CHOP with a siRNA diminished DR5 expression and vernodalol-induced sensitization to the TRAIL treatment. In addition, a c-Jun N-terminal kinase (JNK) inhibitor blocked the vernodalol-induced up-regulation of DR5, indicating that the effect depended on JNK activation. Furthermore, the down-regulation of induced myeloid leukaemia cell differentiation protein (Mcl-1) played an important role in vernodalol/TRAIL-induced apoptosis, as Mcl-1 overexpression prevented this apoptotic effect. Moreover, the vernodalol/TRAIL combination inhibited tumor growth in a xenograft model. Based on our results, vernodalol enhanced TRAIL-induced apoptosis by down-regulating Mcl-1 and up-regulating DR5, and the effects of DR5 depended on JNK activation and CHOP induction. Therefore, combining TRAIL with vernodalol, a naturally occurring agent, may represent a promising therapeutic approach for DLBCL.