LlaBIII, isolated from the naturally occurring plasmid pJW566 from Lactococcus lactis subsp. cremoris W56, encoded a restriction and modification (R/M) system. The plasmid pJK1 carrying the R/M system LlaBIII was transformed into L. lactis IL1403 with type I R/M system located on chromosome and the strain MG1614[pAW601] with AbiS gene on plasmid pAW601, respectively. The transformants obtained showed stacking resistance against bacteriophages. The plasmid pJK1 was transformed into industrial strains L. lactis SMQ86 and CHCC2281, the transformants showed the EOP of the bacteriophages decreased by 10(-3) and 10(-5), respectively. The results indicated that the R/M system LlaBIII could protect strains from bacteriophages in dairy fermentation.