A pharmaceutical for prevention and treatment of demyelination-associated neural function impairing diseases, the pharmaceutical containing erythropoietin as an active ingredient and a method for prevention and treatment of the diseases are provided. The preventive and therapeutic pharmaceutical and method of the present invention protectively act ON the survival of oligodendrocytes, which form a myelin sheath, in cerebrovascular dementia typified by multiple sclerosis and Binswanger disease and diseases involving demyelination. The pharmaceutical and method also promote maturation of undifferentiated oligodendrocytes present in the brain and activating remyelination. Through these mechanisms and the pharmaceutical and method can prevent and treat demyelination-associated neural function impairing diseases.
