We examined over-expression of p53 protein and proliferative activity of neoplastic endocrine and Paneth cells in cancer or dysplasia of ulcerative colitis (UC). The labeling index of p53 or Ki-67 of endocrine cells was counted with double immunostaining of p53 or Ki-67 and chromogranin A (CGA). 540 CGA-positive cells and 65 Paneth cells were all negative for p53. 5.1% of CGA-positive cells and none of 56 Paneth cells were positive for Ki-67 reaction. These observation suggest that even in cancer or dysplasia of UC cell-differentiation to neoplastic endocrine and Paneth cells decrease proliferative activity, and that these types of cell-differentiation suppress over-expression of p53 protein.