The aim of this study was to determine the effect of interaction between tegafur (FT) and epigallocatechin-3-gallate (EGCG) on the expression of α-defensins (HD-5: human α-defensin 5, HD-6: human α-defensin 6) by using a Caco-2 cell line as a model of human intestinal epithelial cells. This is the first study in which the effect of interaction of an oral anticancer drug and functional food on the innate immune system was examined. α-Defensins are abundant constituents of mouse and human paneth cells and play a role in the innate immune system in intestine. We detected HD-5 and HD-6 mRNA in Caco-2 cells and evaluated the effects of FT and EGCG on these mRNA levels. HD-5 and HD-6 mRNA levels were decreased by exposure to FT. Production of reactive oxygen species (ROS) was induced by exposure to FT as well as H₂O₂ exposure, and EGCG suppressed FT-induced production of ROS. Furthermore, FT-induced decrease in HD-5 and HD-6 mRNA levels was almost completely suppressed by EGCG. These results indicate that EGCG restored the decrease of α-defensins induced by FT at the transcriptional level in Caco-2 cells, suggesting that EGCG can be used as adjunctive therapy in chemotherapy.