Objective:To explore the expression of DNA polymerase iota in transitional cell carcinoma cells and tissues; Methods: RT-PCR was applie to detect the expression of polymerase iota in BIU87 and T24 cells, then the expression of polymerase iota was also detected in the same way in transitional cell carcinoma which was derived from clinical bladder carcinoma and renal pelvic carcinoma. Results: The expression of Polt was low in bladder normal membrana mucosa but significantly elevated in transitional cell carcinoma cells. Compared with the expression of polymerase iota in bladder normal mucous membranes, the expression of polymerase iota was significantly increased in transitional cell carcinoma tissue (P＜0.01)and associated with the grade of transitional cell carcinoma. Conclusion: The significantly increased expression of polymerase iota may be associated with the generation and development of transitional cell carcinoma, even with its high heterogenicity.