Ultrasmall superparamagnetic iron oxide (USPIO),as the contrast agent of MRI,possesses two major properties:long half time in the plasma and specific binding with macrophages.Compared with gadolinium,widely-used in clinic presently,USPIO has its unique advantages in diagnosis of central nervous system diseases,though which still need further clinical verification.This article reviews the application of USPIO in MRI diagnosis of some central nervous system diseases.