Abstract: Objective To gain new insight into the immune pathogenesis of ulcerative colitis (UC). Methods Immunohistochemical techniques for T lymphocytes, B lymphocytes and macrophages were used to detect expression of different lymphocyte subsets in biopsy specimens of the colonic mucosa from 50 patients with ulcerative colitis and 5 cases of health control. Results The numbers of T lymphocytes (CD45RO) and Th cell (OPD4) were significantly higher in active UC ( n = 32) than inactive UC ( n = 18 ) or health control ( P ＜ 0.01 ). In comparison to controls, there was no difference in lamina propria B lymphocytes (CD20). Significant difference in macrophages was found between the patients with active UC and patients with inactive UC ( P ＜ 0.01). Conclusion T lymphocytes and macrophages are closely related to activity of UC and provide an immune mechanism for the participation in the acute effect events of tissue destruction. They were important components of immune response network of UC.