The study of eolian deposition in Western Loess Plateau is one of important problems in resent paleoclimatic studies, but the age of the Cenozoic eolian deposition is still in dispute. This study was carried out the rock magnetism, grain size, composition analysis and electron microscope analysis of Fenghuangshan section which is 916 m thick, north of Lanzhou area. The results showed that most of the clay is non-horizontal bedding. The distribution curves, probability cumulative curves and composition characteristics of grain-size, susceptibility, elemental content, morphology of quartz grains of them are similar to those of typical loess, paleosol and red clay samples. So they are eolian deposit, which is the oldest eolian deposit of Cenozoic found in Lanzhou area presently.