Background Immediate intravesical instillation of chemotherapeutic agents after transurethral resection (TUR) of nonmuscle invasive transitional cell bladder cancer has recently been suggested and has been proven to decrease the tumor recurrence rate significantly.This study is to evaluate the efficacy and safety of immediate intravesical instillation combined with regular instillations of Pirarubicin (THP(○R)) as prophylaxis compared to regular instillations only after TUR operation.Methods This was a prospective,randomized,multi-center,clinical study.Patients diagnosed with non-muscle invasive bladder cancer (Ta and T1) pathologically and suitable for TUR were enrolled randomly into two groups.In the study group,the patients received intravesical instillation within 24-hour post TURBT,followed by regular intravesical therapy using 30 mg/50 ml of THP(○R) once a week for 8 weeks,and then once a month to 1 year postoperatively Among the patients.In the control group,patients received regular instillation only.Results A total of 403 patients were enrolled into this study from 26 institutions in China.Among the potients,210 were enrolled into the study group and 193 were enrolled into the control group.At the median follow-up of 18 months,the recurrence rate was 7.8％ in the study group,significantly lower than that in the control group (14.3％; P=0.042).Subgroup analysis showed that the recurrence rate in low and intermediate-risk patients was significantly lower in the study group (6.8％) than in the control group (14.0％; P=0.047),although no significant differences were found in high-risk patients.Conclusion One immediate dose of THP(○R) 30 mg after TURBT followed by regular intravesical therapy appears well tolerated and more effective than regular intravesical therapy for preventing tumor recurrence,especially in low and intermediate-risk patients.