Ki-67 is exclusively present in all stages of cell cycle (C1, S, C2 and mitosis)except for G0, and widely used to determine proliferative activity of various tumors. The relativity of expression of Ki-67 and the biological behaviour of transitional cell carcinoma (TCC) of bladder was evaluated in the study. Methods The paraffin embedded tissue sections from 33 patients with TCC of bladder were reexamined. According to the UICC standard, 21 cases had surperficial tumors and 12 cases had invasive tumors. With the pathological diagnostic standard of WHO, there were 16 cases of G1 , 10 cases of G2 and 7 cases of G3. Meanwhile, there were 21 cases with primary lesions and 12 cases with recurrent lesions. 12 specimens obtained from normal bladders were used as controls. Expres sion of gA 67 was detected by streptavidin-peroxidase (SP) immunohistochemical technique. Results Expression of gA-67 was found in 54. 5%(18/33) of TCCs and 8. 33%(1/12) of controls (P