β-mannanase from Trichoderma reesei was purified by DEAE Sephadex A-50 ion exchange chromatography and Sephadex G-100 gel chromatography. The molecular weight was determined to be 54 kDa by tricine SDS-PAGE. Trigonella foenum-graecum galactomannan was hydrolyzed by the purified β-mannanase, and then the hydrolysates were separated by Bio-Gel P2 chromatography. The main hydrolysates were composed of D.P. (degree of polymerization) 2, 3, and 4, 6 galactomanno-oligosaccharides. To investigate the effects of Trigonella foenum-graecum galactomanno- oligosaccharides on in vitro growth of L. plantarum, were cultivated individually on a modified-MRS medium containing carbon sources such as low- and high-molecular-weight galactomanno-oligosaccharide. Lactobacillus plantarum grew 1.8-fold after treatment with high- and low-molecular-weight galactomanno-oligosaccharides, compared to 1.3-fold for those with standard MRS medium. Bacteriocin was purified by Sephadex G-100 gel chromatography and determined to be 122 kDa by tricine SDS-PAGE. The bacteriocin activated doubly more effectively after treatment with galactosmanno-oligosaccharides compared to those with standard MRS medium. Bacteriocin showed antimicrobial activity against Staphylococcus aureus. The inhibitory compound lost activity when heated to temperatures greater than 30oC and when inhibited to pH changes that lowered the pH below 4 or raised it above 5. Furthermore, its effects were inhibited by treatment with proteolytic enzymes.