Abstract: Objective To explore the diagnosis and treatment of biotinase deficiency (BTD) manifested as encephalomyelopathy. Methods The clinical data of one child with BTD were retrospectively analyzed. The pertinent literatures were reviewed. Results A six-year-old male child suffered from progressive spastic paralysis of lower limbs for 3 months before admission. A similar symptoms occurred after a cold in 3-year-old. It was easy to peel skin on her hands and she had angular stomatitis. Audio visual evoked potential was detected to be abnormal  in other hospital. After hospitalizion, the cerebrospinal fluid examination was normal, and MRI showed long T1 long T2 signals bilateral occipital lobe and basal ganglia region . Because the child represented medulla palsy, and so the tracheal intubation ventilator was administrated to assist ventilation. Urine gas chromatography/mass spectrometry (GC/MS) analysis showed increases of lactic acid, 3-hydroxy acid, 3-tiglyl glycine, methylcitric acid, and ethylene lactic acid. Serum MS/MS analysis showed that the concentrations of propionyl carnitine and 3-hydroxyisovaleryl carnitine were increase obviously. The serum biotinase level was significantly decrease to 0.076 pmol/( min•mm3). The diagnosis of BTD was confirmed. After supplementation biotin , 40 mg/d, the ventilator was successfully weaned on the third day, the child walked again after 2 weeks, and the rash was vanished. After 3 weeks, the head MRI showed disappearance of the original lesion, and there was no abnormal in spinal cord. The BTD gene detected by PCR direct sequencing showed a heterozygosis mutation of T172T/C in the second exon and a homozygous mutation of T1413C in the fourth exon, which was confirmed as a pathogenic mutation by pedigree verification and database query. After discharge, the oral administration of biotin 20 mg/d continued, and no abnormality was found in 2 years of follow-up. Conclusions The manifestations of BTD are complex and diverse. The analysis of urine GC/MS and serum MS/MS can assist the diagnosis. The determination of biotinase activity and gene detection of BTD can further confirm the diagnosis. Timely biotin supplementation has significant treatment efficacy.