A bacterial strain isolated from porcine feces was designated Lactobacillus sp. CPP1 based on 16S rRNA gene sequence analysis. The strain was stable at 120-min exposure to artificial gastric juice (pH 3) and exhibited good viability during 120 min at pH 2.5, maintaining 60% of its initial cell numbers. The strain was resistant to 1% porcine bile extract, and no marked loss of the viability was detected, even during a 4-h exposure. The strain displayed a relatively broad spectrum of antibacterial activity against seven pathogenic indicator bacteria: Enterococcus faecalis, Listeria monocytogenes, Staphylococcus aureus, Escherichia coli K88, E. coli O157:H7, Salmonella typhimurium, and S. enteritidis. Heat-killed Lactobacillus sp. CPP1 enhanced the immune activities of Raw 264.7 murine... macrophages by increasing production of nitric oxide, tumor necrosis factor (TNF)-α, and interleukin (IL)-β, and phagocytic activity. Maximum effects were observed at 1 x 1010 colony-forming units (CFU)/mL of the heat-killed strain. Lactobacillus sp. CPP1 as a feed additive may be a promising alternative to antibiotics in livestock production, because the strain meets the criteria required for probiotics including acid and bile tolerance, antimicrobial activity, and immunestimulatory effects.