The Arnold-Chiari malformation is a congenital abnormality of CNS, characterized by downward displacement the parts of the cerebellum, fourth ventricle, pons and medulla oblongata into the spinal canal. This malformation is one of causative factor of death in neonates and infants. A thorough understanding of the direct and indirect sonographic findings is necessary for diagnosis of Chiari II malformation in the developing fetus. In this case report, we present a Chiari malformation II detected at 23 weeks of gestation by routinely sonographic screening. The Role of prenatal sonography in recognition of the malformation and prognostic value of these features are discussed.