Abstract: Objective To investigate the influence on preventing the relapse of bladder cancer by pirarubicin irrigation ot bladder with different retaining time.Methods Sixty - eight cases of post - operative bladder superficial cancer irrigated with pirarubicin were selected.and divided into two groups randomly.Two weeks after operation pirarubicin bladder irrigation began.After every irrigation a well stabilized indwelling air - bulb catheter was used and the patient's lying posture changed routinely.The pirarubicin retaining time of these two groups were 15 minutes and 30 minutes respectively.Every time 20 mg of pirarubicin were used.This was done once every week and lasted for eight weeks.After this the irrigation is done once every month,and continued for 1 year.The patients'survival time and relapse rate were observed and compared.Results The average survival time of the first group was 15 months,while that of control group was 11 months.The relapse rate of the control group was 38. 24% and it was by far higher than that of the first group ( 14.71% ).The difference was significant. Conclusions The prevention of post - operative bladder cancer relapse - by pirarubicin bladder irrigation with a retaining time of 30minutes is a very satisfactory method.The relapse rate is lower than that of only retaining 15 minutes.Use of an indwelling air - bulb catheter can protect the urethra from chemical injury.It is worthy widely spreading.