Cerebrospinal fluid rhinorrhea is rare problem, which is a flow of the cerebrospinal fluid from the nasal cavity. Its causes are classified as non-traumatic and traumatic, the latter is common. Recently we experienced a cases of C.S.F. rhinorrhea in a 31-year-old male who had been clear, watery nasal discharge. Its cause was indentified a cerebral astrocytoma at left frontotemporal region by several specific examination. So we present a case of the C.S.F. rhinorrhea with its concerning literatures.