The gamma-aminobutyric acid (GABA) in the digestive system of Chlamys farreri was analyzed by immunohistochemical ABC staining. The results showed that GABA-positive cells existed widely in the epithelium of labellum, labia oris, and intestine. Besides, the positive granules were centralized in the dissociative sides of epithelium. There were no GABA-positive cells in the epithelium of stomach. Positive cells were also observed in both the epithelium and connective tissue of hepatopancreas, and some of them were accumulated in lumps in the epithelium. It can be concluded that GABA is abundantly distributed in the digestive system in C.farreri and it may be involved in the regulation of digestive function.