The key role of cathepsin D and B is intralysosomal digestion of used cellular proteins and other proteins that enter cells through endocytosis. Under pathological conditions like cancer formation and growth, cathepsins from lysosomes are released. The aim of the study was to determin of cathepsin D and B activities in serum of patients with urothelial bladder cancer depending on disease severity and determination of its' changes after transurethral resection of tumor.Experiment involved 50 patients. Blood samples were obtained from 18 healthy volunteers and 32 urothelial bladder cancer patients. Samples from people with suspected urothelial bladder cancer were collected three times: before the surgery, 2 weeks and 6 weeks after the surgical treatment.Our research showed that cathepsin D activity, measured as the level increment of acid soluble tyrosine, is the highest before the surgery in muscle invasive bladder tumor (pT2) (57,9 nmol/ml). 2 weeks and 6 weeks after the surgical treatment, cathepsin D activity is decreased. In case of cathepsin B activity, measured as the level of released p-nitroaniline, decreased, 2 weeks and 6 weeks after the surgical treatment in both cases of disease severity.Cathepsin D and B activities in the serum of patients with urothelial bladder cancer are directly proportional to disease severity and significantly higher compared with control group. Transuretral resection of the tumor leads to diminution of their activities in second and 6th week after the procedure.