Lactoferrin (LF) is an iron-binding glycoprotein contained in milk, tears, saliva, nasal secretions, blood plasma, and secondary granules of neutrophils that plays important roles in host defense1). Infections by rhinoviruses or coronaviruses, the main pathogens of common colds, increase the endogenous synthesis of LF in humans, which suppresses respiratory tract infections via its antiviral and immunomodulatory effects2～3). LF is present in the milk of most mammals. Human LF (hLF) accounts for approximately 20% of the protein content in human milk, and plays important roles in the host defense of infants4). The amount of bovine LF (bLF) in cow milk is approximately one-tenth of that of hLF in human milk and bLF is easily denatured by heat sterilization, making it difficult to take it from commercial milk and dairy products. Recently, bLF is isolated from cheese whey and skimmed milk, well sterilized without denaturation, and added to formulas, yogurt, drinks, and supplements5). Orally ingested exogenous bLF is expected to exert antiviral effects in the digestive tract and upper respiratory tract (pharynx), immunomodulatory effects in the small intestine, and suppress respiratory and gastrointestinal tract infections. In this review, we summarize the antiviral effects of LF against respiratory and gastrointestinal viruses, the immunomodulatory effects of bLF, and clinical trials of bLF on respiratory tract and gastrointestinal infections.