Boneless pork chops were vacuum-packaged at the various degrees of vacuum to have 4 different levels (17.6%, 9.8%, 3.1% and 0.4%) of initial residual oxygen in the packages. During the storage period of 21 days at 4℃, changes of reisdual oxygen content, total bacteria count, psychrotrophs count, anaerobes count, lactic acid bacteria count and fluorescent pseudomonads count were investigated. At the end of storage period, all treatments showed no difference in both psychrotrophs and lactic acid bacteria count. However, control gave the highest numbers in total bacteria, anaerobes and fluorescent pseudamauads count. According to results obtained from this study, it appeared that high vacuum-packaging would be more practical method than the other three in terms of microbiological shelf-life.