Cortex mori (Morus alba L. : Sangbaikpi), the root barks of mulberry tree, has been used as an antiphlogistic, diuretic, and expectorant in herbs. Previous studies have demonstrated that the phenolic extracts of Cortex mori have hypotensive, hypoglycemic, antifungal, antiviral, antiinflammatory, and anticancer effects, and the hot water extract from Cortex mori has the inhibitory effects on compound 48/80-induced mast cell degranulation and histamine release from rat mast cells (RMCs). Colchicine, an alkaloid found in the crocuslike plant, has been known as an inhibitor of mitosis and microtubule assembly by formation of tubulin-colchicine complex. The purpose of this study was to examine the effect of Cortex mori on the colchicine-induced mast cell degranulation, histamine release, and calcium uptake as a part of the study of the role of microtubules in the mast cell secretory process and the inhibitory mechanism of Cortex mori. The results were summarized as follows. Cortex mori sigificantly inhibited the colchicine-induced cytomorphologi-cal changes of RMCs such as displacement of the nucleus to the periphery, pronounced anisodiametry of the cytoplasm, stubby or broad cytoplasmic mass. Colchicine induced histamine release from RMCs and calcium uptake into RMCs, but it was not significantly , compared to those of negative control group. Cortex mori inhibited the colchicine-induced histamine release from RMCs and calcium uptake into RMCs. Above results, it is suggested that Cortex mori has an activity to inhibit the colchicine-induced cytomorphological changes by inhibition of calcium uptake into the mast cells.