Objective　To explore the clinical characteristics of CASK gene mutation. Methods　The clinical data and gene test results of a child with mental retardation, microcephaly and pontocerebellar dysplasia caused by CASK gene mutation were reviewed. Results　The male patient was 3 months and 27 days old. The main clinical manifestations were microcephaly, congenital laryngeal cartilage dysplasia and tracheomalacia, growth retardation, feeding difficulties, high limb muscle tension and repeated convulsions without fever. Chromosome microarray analysis did not detect clinically significant gene copy number deletion, duplication and large fragment homozygote phenomena. High-throughput sequencing and Sanger sequencing showed that the children carried a hemizygous frameshift mutation in CASK gene, c.1818_1821dupAACT, p.t608nfs *16, which was a possible pathogenic variation. Conclusion　A case of mental retardation, microcephaly and pontocerebellar dysplasia caused by CASK mutation was found.