Abstract: The authors analysed the gum flora of rats qualitatively and quantitatively by magnetic bar dilution method. The results showed that in conventional and SPF rats the dominant bacteria were: micrococcus, streptococcus，corynebacterium and propionibacterium，with isolation rate more than 70%, The results suggest that the SPF rats are more suitable for oral disease study as they are less in individual difference in gum flora than those of the conventional ones.

Key words: Magnetic bar, Dilution method, Gum flora, Rats, Conventional SPF