Abstract: Objective To explore the clinical characteristics of neonatal-onset carbamoyl phosphate synthetase I deficiency (CPS1D). Methods Clinical data and result of genetic detection of one neonate with CPS1D were retrospectively analyzed. The pertinent literature was reviewed. Results A 3-day old girl, with onset symptoms of nonspecific performance, such as poor feeding, less activity, tachypnea, and seizures. After fasting, anti-infection, and respiratory support etc. the condition was improved. However, the condition deteriorated and developed rapidly after feeding restarted. MRI showed extensive cerebral white matter lesions. Blood ammonia?>?500 μmol/L. Gene detection found two heterozygous mutations in pathogenic gene CPS1 in twentieth exon of c.2407C?>?G (p.803, R, G) and fourth exon C.323G?>?A (p.108, G, E), according to which CPS1D was diagnosed finally. Conclusions For neonate with normal birth, had feeding difficulty, seizures, and consciousness disorder after establishment of normal feeding, if blood ammonia level significantly increased, the blood and urine amino acids analysis and gene detection should be performed to confirm the diagnosis.