The effect of different initial concentrations of O2 in modified atmosphere packaging on the growth of microorganism from chilled meat was investigated.The mixed strains from chilled pork were inoculated into the liquid medium which were packaged with different concentrations of O2.The samples were stored at 3℃ and the number of Pseudomonas,Enterobacteriaceae,Lactic acid bacteria and total number colonies were collected at different time during the storage.The results demonstrated that the initial concentration of O2 showed little influence on these microorganism when it was changed from 11.0% to 79.0%.And the low concentration of O2(0.3%～11.0%) could effectively curbed the growth of the microorganism,the lower the concentration the heavier the inhibition.The order of the inhibition effect from the strongest to the weakest was total number colonies,E.coli,Lactic acid bacteria and Pseudomonas.