Objective　To investigate the clinical features and gene mutations of 3M syndrome. Method　The clinical data of a child with 3M syndrome was retrospectively analyzed. The DNA was extracted from the peripheral blood of the child and parents, and the sequence analyses were performed by Agilent SureSelect exon capture and Illumina HiSeq sequencing platform. And the mutant gene was validated by Sanger sequencing. Results　The six-month-old girl presented special face and growth retardation. The girl had a missense mutation c.4898C>T, p.T1633M in the CUL7 gene (NM_014780.4), and both her parents had heterozygous mutations. The girl was diagnosed with 3M syndrome. Conclusions　The CUL7 mutation is the major causative gene of 3M syndrome in this girl. Early gene testing should be performed to confirm the diagnosis in suspected clinical phenotype.