Previous studies have revealed that ingestion of bovine colostrum is effective in preventing pathogens from invading through the gastrointestinal tract (GI) and modulating the mucosal immunity of the GI tract, indicating that its effect is principally local. Thus it is unclear if ingestion of bovine colostrum can affect the systemic immune system. In this study, we investigated the effect of taking bovine colostrum (vs phosphate-buffered saline) for 14 days on the behavior of the immune cells of mice. Isolated splenocytes, which are pivotal cells of systemic immunity, were then stimulated with Escherichia coli lipopolysaccharide. Bovine colostrum significantly reduced NK cell and monocyte activities and lymphoproliferaltive responses to LPS stimulation. Thus dietary bovine colostrum renders immune cells less responsive to LPS stimulation. Dietary bovine colostrum thus affects the systemic immune system and may have anti-inflammatory actions.