Objectives: Intravesical treatment with mitomycin C (MMC) after trans-urethral resection of bladder tumor is indicated by the guidelines of the European Association of Urology and the American Urology Association. MMC solution is highly irritative to skin and mucous membranes and may be of potential harm to staff handling it. We describe a closed-system device that we have developed for MMC intravesical instillation immediately after transurethral resection of bladder tumor (TURBT) for bladder cancer. Material and Methods: A design was developed based on three requirements of a closed system for intravesical instillation of cytotoxic drug: (1) the connection of the system with the MMC administration device (e.g., syringe) must prevent any spillage or spraying of the drug solution. (2) the system should automatically close in the absence of a syringe at the connecting hub.(3) the system should have a draining mode to enable rapid drug and urine drainage into a commercially available urine bag using conventional attachments. Results: In the system developed, MMC syringe is screwed to the connector. The valve is directed to the urinary bladder, and the MMC is injected. At the end of the therapy, the valve is directed to the collecting bag and the MMC and connector are disposed according to the guidelines for hazardous material disposal. Conclusions: To our knowledge, this is the first report of a closed system specifically designed to reduce staff exposure during instillation of MMC. No single case of MMC spill or occupational exposure has been reported since the closed system was introduced.