Tryptase has been considered as a cellular marker of mast cells in the tissuse of human and some mammalian species To detect frog mast cells whether or not contain tryptase in thire cytoplasm, a murine monoclonal antibody (AA1), raised against human mast cell tryptase , was used in an indirect immunoperoxidase technique to stain the paraffin sections of intestine, spleen and tongue collected from bullfrogs（Rana catesbeiana） and sqamous cell carcinoma tissue of esophagus (as a positive control) from an adult man. It was firstly demonstrated that the frog mast cells contain tryptase in their cytoplasm and an excellent cross-reaction of the antibody AA1 with frog mast cell tryptase was obtained from the Boun’s fluid fixed frog tissues. In frog tissues the tryptase-positive mast cells mainly lie in lamina propria of intestine, a little were distributed in the base of intestinal villus and around submucosal glands of tongue and none were found in the spleen. There were lots of tryptase-positive mast cells in the mesenchyme of the human carcinoma tissue of esophagus. In conclusion, like human mast cells, bullfrog mast cells also contain the special enzyme, tryptase and it was likely that bullfrog can be used as an ideal experimental animal for the study of mast cell biology.