Objective To establish an orthotopic rat model of bladder cancer induced by N-methyl.nitrosourea (MNU)and to evaluate the diagnostic value of CT(computed tomography)scanning in this experimental model.Methods 50 SD rats were randomly divided into the control group(group A)with 15 rats and experimental group(group B)with 35 rats.Each rat of group B was treated with 2 mg MNU per dose every other week,totally 4 doses,by per urethra administration.Meanwhile,each rat of group A was treated with normal saline.Then,at the 14th week,all the rats were evaluated by CT scanning and pathological examination.Results Abnormal changes were detected in each of the 28 rats in group B by CT scanning,and manifested as local mass,thickening bladder wall accompanied with heterogeneous density.Bladder cancer was diagnosed by pathology.However,no bladder tumor was detected by CT scanning and pathologicalexamination in group A.Conclusion A rat model of orthotopic bladder cancer can be established by per urethra administration of MNU.CT scanning is a reliable diagnostic technique concerning this model.Furthermore,this technique can render US a more suitable rat model for further experimental studies on chemotherapy and radiotherapy of bladder Cancer.