Immunohistochemical localization and morphology of 5-Hydroxytryptamine immunoreactive cells (5-HT cells) in the digestive tract of Gloydius shedaoensis have been investigated by using the ABC(avidin-biotin-peroxidase complex)immunostaining technique. The 5-HT positive immunoreactive cells could be observed throughout the digestive tract, from esophagus to rectum. The density curve appeared wavelike and the cell density (number/field of vision) was the highest in the cardiac part of stomach (7.15±2.38), followed by the pylorica part of the rectum (4.55±3.14), and the lowest cell density was found in the esophagus (1.2±0.71).The 5-HT cells distributed at the bottom of epithelial cells, between epithelial cells, between glandular epithelial cells or in the lamina propria. The 5-HT cells had different shapes including round, shuttle-like, tapering and other shapes. We suggest that 5-HT positive immunoreactive cells in the digestive tract of G.shedaoensis should have both endocrine and exocrine functions, and the distributive density is related to its feeding habit and life environment in G.shedaoensis.