The genetic relationship of six Lactobacillus strains and five laboratory isolated form fermented milk were determined by a random amplified polymorphic DNA(RAPD)-Polymease chan reaction (PCR) method. With 42 random primers. the result were analyzed by using the NTSYS-PC software for phenetic analysis. it revealed that all tested bacteria were divided into three distinct clusters. The clusters implied three subgenuses existed for the genus Lactobacillus, which were previously proposed by Rogosa and Sharpe. From the results, it was also possible to determine that the isolated Lactobacillus strains from fermented milk were grouped into L. acidophilus or L. bulgaricus. Interestingly. the three tested L. casei strains were divided into different clusters implying different subgenuses, i.e., Thermobacterium (L. casei YIT 9018) and Streptobacterium(L. casei CHR. Hansen and L.casei ATCC 4646). According to the distance matrix generated by an UPGMA program, the isolated bacteria LT01 and LT02 were determined as a subspecies of L. bulgaricus. The HK01, HK02 and HK03 were very closely related to either L. acidophilus or L. case YIT 9018. Hence, RAPD-PCR appears to be a very practical method to determine the genetic relationships of the Lactobacillus species and to characterize the unknown Lactobacillus strains at the subspecies level.