The adsorption rates of Lacticin LLC518 on Lactococcus lactis subsp.lactis 518 at different pH conditions were studied.The results showed that the adsorption rate was 100% at pH 6.0 while no Lacticin LLC518 was adsorbed at pH 2.0.Therefore,the crude Lacticin LLC518 was prepared from the cell-free supernatant of the L.lactis subsp.lactis 518 culture when the exterior environment had a pH of 6.0 and 2.0 by absorbing and desorbing Lacticin LLC518,respectively.The pH absorption method has an obvious advantage superior to the ammonium sulphate precipitation method for its better absorption effect when the crude Lacticin LLC518 from precipitation with ammonium sulfate as a control.The specific activity of Lacticin LLC518 was increased 83.02 fold with a yield of 20%.