Grimelius' silver nitrate stain was used to investigate the morphology and distribution of argyrophilic cells in digestive tube of the Mexican Medical Leech (Poecilobdella manillensis). The distribution density of argyrophilic cells was counted according to the distribution characteristics. All the measured data were compared with Duncan multiple comparison using spss 17.0. The level of significant difference was set at P < 0.05. The results showed that argyrophilic cells did not exist in esophagus (PlateⅠ: 5), but distributed throughout most of the other portions in different densities (PlateⅠ). These cells were stained with brownish or black in the digestive tube. Argyrophilic cells in epithelium of lips had apophysis pointing to the oral cavity, and some of them had distinct cytoplasmic processes and inner cell visible black particles (PlateⅠ: 1). Argyrophilic cells were observed in the jaw, with shapes of circle, ellipse, strip and so on (PlateⅠ: 2, 3). Most argyrophilic cells in epithelium of crop and villus epithelium of intestine had apophysis pointing to the crop or intestine (PlateⅠ6﹣8), while a minority stretched their processes to the lamina porpria (PlateⅠ: 9), indicating the possible luminal secretion and endocrine functions of these cells. The density of argyrophilic cells in the jaw was the highest (117.63 ± 14.08), while that in the rectum was the lowest (2.63 ± 0.91). There was extremely significant difference between the two parts (P < 0.05). No argyrophilic cells were also observed in the esophagus (Table 1). Based on these results, we inferred that the morphology and distribution of argyrophilic cells in the digestive tube might be closely related to the feeding and digestive physiological activities of this leech.