Abstract: The purpose of this study is to investigate the potential antimicrobial effect of non-dialyzed, dialyzed and freeze-dried whey against S. enteritidis and the effect of storage condition on lactoperoxidase (LPO) activity. The LPO activity of all forms of whey was studied at -20, 4 and 25°C during 4 weeks storage for LPO activity. The results showed that all forms of whey had antimicrobial activity against S. enteritidis. The various forms of whey had no remarkable differences on the antimicrobial activity. When all forms of whey was stored at 25°C, their LPO activity terminated within 2 weeks or less. LPO activity of non-dialyzed and dialyzed whey when stored at 4°C, decreased remarkably within 4 weeks. However, the decrease of LPO activity during 4 weeks storage was not found in freeze-dried whey. All forms of whey stored at -20°C kept a stable LPO activity for 4 weeks. These results suggested that whey (non-dialyzed and dialyzed) and freeze-dried whey should be stored at 4°C or less, in order to keep LPO activity.