Abstract: The mass transfer problem of oxygen in a plate membrane oxygenator without oxygenation was studied. For oxygen-blood system the mathematical model was presented. It was established on the basis of mass transferring chracteristics of oxygen in blood medium and resulted by the method of mathematical developing, i. e. by solving the relevantdifferential equations of diffusion. The theoretical expression of dimentionless average concentration and Sherwood number were obtained in this way and the results was apparently supported by experimental facts in a silicone membrane oxygenator.The dimentionless correlation is given as follows:(?)_(LO)=0.055 Re~(0.59)Sc~(0.33)which, according to authors' opinion, can be used with advantage in the designing work of plate membrane oxygenator.