PROBLEM TO BE SOLVED: To provide an α-defensin secretion promoting agent and an antimicrobial agent, which are highly safe for living organisms and comprise as their effective ingredients naturally occurred active ingredients that increase the antimicrobial α-defensin contents in vivo.SOLUTION: The present invention provides α-defensin secretion promoting agent and an antibacterial agent, which contain barley leaves, stems, and/or processed products thereof. The α-defensin secretion promoting agent and the antimicrobial agent are expected to improve, relieve, recover, treat, and prevent various diseases and abnormalities related to the abnormalities of gastrointestinal tissues, such as digestive tract immunodeficiency, harmful microbial metabolites in the gastrointestinal tract, and harmful enzyme production.SELECTED DRAWING: Figure 1