Distribution and morphological characteristics of mast cells in gastrointestinal tract of Tilapia Galilaea were studied by modified toluidine blue staining. The results showed that the mast cells scattered or concentrated in the lamina propria mucosa and submucosa, especially around small blood vessels (Fig. 1). Mast cells varied in their sizes and shapes. They were round, oval, fusiform or rhombic in shape, and their nuclei were in dark blue when stained with toluidine blue, and the granules were in purple red with varying shades of color (Fig. 2). Statistical analysis (Table 1) by one-way ANOVA of SPSS 24.0 showed that the number of mast cells in stomach (9.7 ± 1.9), pyloric caecum (8.3 ± 2.8), hindgut (8.3 ± 1.8), foregut (6.3 ± 1.9) and midgut (5.1 ± 1.8) of Tilapia Galilaea decreased in turn. The number of mast cells in gastric and pyloric caecum was significantly higher than that in foregut or midgut (P < 0.05), but there was no significant difference from that in hindgut, and the number of mast cells showed no significant difference in the foregut, midgut and hindgut. In conclusion, mast cells were mainly distributed in the lamina propria and tunica submucosa of various gastrointestinal tissues, with different sizes and shapes, and the number of mast cells decreased successively in the order of stomach, pyloric caecum, hindgut, foregut and midgut.