Abstract: Objective: To study the selective killing effects of immunotoxin BDI-1-PEA against human-bladder cancer cell line E-J. Methods: Bladder cancer cell line E-J cells were incubated with immunotoxin BDI-1-PEA, BDI-1 and the mixture of BDI-1 and PEA. MTT was used to measure the killing ratio of different drugs at different concentrations. Balb/c mice bearing human bladder cancer was divided into three groups, with 10 each group, when the tumor size reached 0.3 cm in diameter, BDI-1-PEA, BDI-1 and IgG of mice were injected individually to each group through the tail vein every other day for 6 times, and measure the tumor size with compasses daily for 21 days. The conjugating BDI-1-PEA was poured into bladder to 24 postoperative bladder cancer patients 2 times a week for 4 weeks as the targeted immunotoxion therapy. All patients have been followed up with cystoscope and USB every 3 months. Results: The studies in vitro indicated that BDI-1-PEA conjugate showed a stronger selective cytotoxicity against human bladder cancer cell line E-J compared to BDI-1 or IgG of mice. The difference was significant in comparison with cytotoxicity against non-target cell line (P<0.01). In 24 patients given BDI-1-PEA, only 2 patients recurrence after followed up 7~22 months, with an average of 15 months. Conclusion: Those results suggest that BDI-1-PEA conjugate shows selective killing effects against human-bladder cancer cell, and beneficial effects for preventing postoperative recurrence of the bladder cancer.