The study of Juglans regia water extract effect on leukocyte count in peripheral blood has been performed on leukopenia experimental model obtained by single injection of cyclophosphan in nonlinear mice. Different ways of administration were used. We also studied the effect of walnut extract on some parameters (NO, catalase) of antioxidant system and prooxydative processes. It has been established, that the correction of myelopoiesis suppression can be achieved only by taking the walnut water extract perorally. It also has been shown, that in response to single injection of cyclophosphan the walnut extract can change the activity of catalase and correct the antioxidant activity. The extract of Juglans regia also causes the quantitative changes of NO and thus, corrects the enhanced oxidative processes.