This study investigated the distribution, localization and expression of 4 kinds of sex-steroid hormone receptors in 7 parts of the gastro-entero-pancreatic system in bullfrog, Rana catesbeiana, and discusseds the roles of these 4 kinds of sex-steroid hormone receptors. Tissue samples were taken from 7 parts of the gastro-entero-pancreatic system including esophagus, stomach, duodenum, jejunum, ileum, rectum and pancreas. Paraffin sections and Strept Avidin Biotin-peroxidase Complex (SABC) immunohistochemistry techniques were used to reveal 4 kinds of sex-steroid hormone receptors with antisera including rabbit anti-estrogen receptor α (ERα), estrogen receptor β (ERβ), androgen receptor (AR), progesterone receptor (PR) primary antibodies. Sections were re-stained by haematoxylin to localize the distribution of sex-steroid hormone receptors. Sections not re-stained by haematoxylin were used to analyze the optical density of positive reaction products, and the mean optical density was calculated by Image-Pro Plus. All the data of mean optical density were analyzed by using SPSS 19.0. Mean optical density values of each sex-steroid hormone receptor in 7 parts were analyzed using one-way ANOVA. The results showed that all 4 kinds of sex-steroid hormone receptors were expressed in the gastro-entero-pancreatic system of bullfrog, and there was no obvious difference in the distribution pattern between female and male bullfrogs. Estrogen receptor α (ERα) mainly distributed in stomach gland, lamina propria of rectum and pancreas (Fig. 1). Estrogen receptor β (ERβ) mainly distributed in esophagus epithelium, lamina propria of rectum and pancreas (Fig. 2). Androgen receptor (AR) mainly distributed in esophagus epithelium, rectum and pancreas (Fig. 3). Progesterone receptor (PR) mainly distributed in esophagus epithelium, jejunum and pancreas (Fig. 4). Negative controls of esophagus, stomach, rectum and pancreas staining were also displayed (Fig. 5). Optical density analysis (Table 1) displayed that estrogen receptor α (ERα) had the strongest positive reaction in the stomach and rectum of bullfrog, and relatively weaker reaction in the pancreas. Estrogen receptor β (ERβ) had the strongest positive reaction in the rectum, and relatively weaker reaction in the esophagus and pancreas. Androgen receptor (AR) had the strongest positive reaction in the esophagus, and relatively weaker reaction in the rectum and pancreas. Progesterone receptor (PR) had the strongest positive reaction in the jejunum and relatively weaker reaction in esophagus and pancreas. The positive immunoreactivity of estrogen receptor α (ERα) in stomach and androgen receptor (AR) in esophagus, rectum was stronger in the female than in the male. The positive reaction of estrogen receptor β (ERβ) in pancreas was stronger in the male than in the female. Finally, we summarized that estrogen receptor α (ERα) and estrogen receptor β (ERβ) distributed most predominantly in the gastro-entero-pancreatic system, followed by androgen receptor (AR) and progesterone receptor (PR). And these 4 kinds of sex steroid receptors were mainly distributed in the esophagus, stomach, rectum and pancreas, especially in stomach, and rectum. The distribution of 4 kinds of sex-steroid hormone receptors in the gastro-entero-pancreatic system of bullfrog implicated that sex-steroid hormones might have multiple regulatory roles in the digestive function of bullfrog, especially in the function of stomach and rectum.