Microflora in the contents of intestinal tracts of Bullfrog at different stages of its development was investigated using 7 different agar media, and major bacterial components were as follows: Tadepoles, Bacteroides A-like, other Bacteroidaceae, helically coiled and filamentous rods, Pseudomonas, A. hydrophila and pin-hole colony formers; metamorphosing tadpoles with hind legs, Bacteroides A-like, other Bacteroidaceae, Clostridium and pin-hole colony formers; frogs, Bacteroidaceae, Clostridium, C. freundii, C. diversus, E. coli, E. hafniae, K. pneumoniae, A. hinshawii and P. shigelloides. The differences of the intestinal microflora may depend on the changes of physiological conditions of host animals, and it is found that frogs is an important experimental animal to study the interaction between the intestinal microflora and host animals.