The antimicrobial activity of Leuconostoc lactis BT17, isolated from a spontaneously fermented cereal beverage (boza) against some test microorganisms (Escherichia coli ATCC 25922, Salmonella sp. and Klebsiella pneumoniae) was determined by co-culturing of the strain Leuconostoc lactis BT17 with each of the test microorganisms under static conditions. It was found that the strain Leuconostoc lactis BT17 inhibited the growth of the test microorganisms and no viable cells of Escherichia coli, Salmonella sp. and Klebsiella pneumoniae were detected at the 48-th hour of the co-culturing. The reduction of the number of viable cells in the mixed populations was a result of the produced lactic acid by Leuconostoc lactis BT17 in the culture medium, which modify the conditions unlikely to growth of the test microorganisms.