Objective: To investigate clinical, laboratory tests and imaging features of three patients with creatine deficiency syndromes caused by GAMT gene mutation. Methods: Clinical, brain MRI features, urine creatine and brain MRS results of patients were retrospectively analyzed, that gene mutations were identified by targeted capture technology and next generation sequencing. Results: Three patients, one male, two females (sisters), age from 9 months to 7 years old, had growth and mental retardation. Two of them had varying degrees of autism-like behaviors and seizures. Brain MRI showed one case was normal, the other had symmetric patchy slight long T1, long T2 signal in bilateral globus pallidus and dorsal pons, another case had symmetric long T1 and long T2 in dorsal pons. Brain MRS showed creatine reduced in bilateral basal ganglia and frontal lobe. Urinary metabolites examinations showed urine creatine was significantly decreased, urine guanidinoacetate was increase, and urine creatinine was normal. Two heterozygous mutations were found in GAMT gene screening of the boy, a paternal c.467C>A, which reported pathogenic previously, and maternal c.194T>C. Another two girls had c.328-1C>T homozygosis mutations. c.194T>C and c.328-1C>T had not been described previously, function prediction was probably damaging. Conclusion: Patients with creatine deficiency syndromes due to GAMT mutations begin with the symptom of development retardation. Abnormalities of globus pallidus and pons on brain MRI, urine creatine examination and brain MRS may help the diagnosis.