A strain,Lactobacillus acidophilus NX2-6,was isolated from Chigee,having ability of producing broad-spectrum antimicrobial substance.Precluding the effect of organic acids and hydrogen peroxide,the fermentation broth of strain NX2-6 exhibited significant inhibitory activity against gram-positive bacteria,such as Staphyloccous aureus;gram-negative bacteria such as Escherichia coli and fungi such as Aspergillus oryzae.After treated with trypsin,pepsin,protease K and α-chymotrypsin,it's antimicrobial substances inhibitory activity decreased sharply with all of them but α-chymotrypsin,which showed the antimicrobial substance might be a protein or a mixed substance.The antimicrobial substance showed good thermal stability in antimicrobial activity within the range pH 2.0-5.0,with the optimum activity at pH 2.0.So it indicated the antimicrobial substance,termed Lactobacillin NX2-6,belongs to a bacteriocin.The substance produced by strain NX2-6 was a promising cadidate applicable in the bio-control and food industries.