Luteolin has been reported to possess apoptotic and antitumor properties. Apoptosis induced by endoplasmic reticulum (ER) stress becomes a potential target for chemotherapeutic strategies since drug resistance develops less if anticancer action is attributed to this apoptosis. In the present study, we raised a possibility that luteolin may induce apoptosis via inducing the ER stress and attempted to test this possibility using HT-29 human colon cancer cells. When HT-29 cells were treated with luteolin, decrease of cell viability, DNA fragmentation and the increase of sub-G1 population were observed, confirming that this compound induced apoptosis. Simultaneously, the cells showed typical signs observed in the response of ER stress, which were Ca2+ overloading in cytosol and mitochondria, phosphorylation of PKR-like ER kinase (PERK) and its downstream proteins: eukaryotic initiation factor-2α and inositol requiring protein1(IRE1), splicing of ER stress-specific X-box transcription factor-1 (XBP-1), cleavage of activating transcription factor 6 (ATF6) as well as up-regulation of glucose-regulated protein-78 (GRP78) and CCAAT/enhancer-binding protein-homologous protein (CHOP). However, when HT-29 cells transfected with siCHOP RNA were treated with luteolin, its effects on decrease of cell viability, DNA fragmentation and sub-G1 population were significantly reduced, suggesting that the luteolin-induced apoptosis is mediated by inducing ER stress. These results support that luteolin has the potential as an agent for cancer prevention or treatment.