A membrane system for the purification of blood by reactive hemodialysis was realized. The device consists of a conventional hollow-fiber dialysis module connected to a batch stirred enzyme reactor. Attention was focused on the removal of uric acid by the enzyme urate oxidase. The kinetics of the enzyme-catalyzed reaction was investigated in a laboratory reactor, at different temperature and pH conditions, and in a wide substrate concentration range. Then reactive dialysis tests were carried out. The results obtained showed high removal degrees (up to 70%, after four hours), even when limited amounts of enzymatic solution were used. A simplified mathematical model of the removal process was developed. The model was used to interpret the experimental results and to predict the removal degree attainable upon treatment of blood by the process proposed.