Objective To compare and explore the morphological characteristics of mast cells in different tissues of 6 types of common laboratory animals. Methods Ten healthy adult SPF Kunming mice, 10 SD rats, 10 Hartley guinea pigs, 10 New Zealand rabbits, 6 beagle dogs and 6 Macaca mulata (male:female=1:1, for all) were used in this study. The animals were sacrificed by euthanasia, samples of the skin, lung, spleen and sigmoid colon were taken from mouse, rat, guinea pig, rabbit, dog and monkey, and fixed in formalin and Bouin's solution. Paraffin sections were stained with toluidine blue and Alcian blue-safranin O, respectively. The mouse skin and dog spleen were immunohistochemically stained for substance P. A color pathological image analysis system was used to conduct the analysis of morphometric parameters of mast cells. Samples of the skin of these animals were also fixed in glutaraldehyde for the electron microscopic observation and comparison of the mast cells.Results Mast cells in different types of animals were distinctive in distribution, morphology, size, metachromasia and staining properties. Density and morphometric parameters of the mast cells had significant differences among the 6 types of animals (P<0.05). Characteristic granules were contained in the skin mast cells of guinea pig, dog and monkey. Mast cells in the mouse skin, dog spleen and nerves in the mouse skin showed immunoreactive substance P.Conclusions Mast cells in the 6 types of laboratory animals showed histochemical and morphological heterogeneity, which have important reference values in animal experimental research on mast cell function.