BACKGROUND AND AIMS Epithelial barrier dysfunction plays a critical role in the initiation of a number of immune diseases; the causative factors are not fully understood. The present study aimed to elucidate the mechanism by which the eosinophil-derived interferon (IFN)-lambda induced the gut epithelial barrier dysfunction. METHODS The duodenal biopsies were obtained from patients with or without food allergies. The eosinophils and IFNλ expression were observed by immune staining. Intestinal epithelial cell line, T84 cells, and a mouse model were employed to observe the effect of IFNλ on the epithelial barrier function and the initiation of skewed T helper (Th)2 polarization in the mouse intestine. RESULTS IFNλ expression was observed in over 80% human eosinophils of the subjects with or without food allergies. Exposure to microbial products, lipopolysaccharide or peptidoglycan, could induce eosinophils to release IFNλ. Exposure to IFNλ could induce intestinal epithelial barrier dysfunction via inducing the epithelial cell apoptosis. Concurrent exposure to microbial products and food antigens could induce aberrant antigen specific Th2 polarization and Th2 pattern inflammation in the intestine. CONCLUSIONS Eosinophils express IFNλ that can induce intestinal epithelial barrier dysfunction and promotes the initiation of the aberrant Th2 polarization in the intestine.