The clinical data of a case with late-onset isolated sulfite oxidase deficiency(ISOD)admitted in the Department of Neurology, Children′s Hospital, Zhejiang University School of Medicine in July 2021 were retrospectively analyzed.Fifteen previously published cases of late-onset ISOD were also reviewed.The patient was a girl, who was hospitalized because of " motor regression with mental retardation for 5 days" at 1 year old.The manifestations of the patient were extrapyramidal symptoms, regression of motor development and seizures.The level of urinary sulfites in the patient was increased.Magnetic resonance imaging (MRI) features were bilateral pallidus and substantia nigra.Gene sequencing suggested a pure missense mutation of the sulfite oxidase( SUOX) gene c. 650(exon5)G>A(p.Arg217Gln). In 16 cases of late-onset ISOD, the median age at onset and diagnosis was 10.5 months and 34.0 months, respectively.The common clinical manifestations were hypotonia (13 cases), seizures (10 cases), movement disorders (9 cases), and ectopia lentis (6 cases). The most common brain MRI feature was pallidus changes (11 cases), followed by lesions of substantia nigra (5 cases), and cerebral atrophy (4 cases). Fourteen cases of late-onset ISOD showed a positive urinary sulfite test.The missense mutation of the SUOX gene was found in 9 cases.It suggested that brain MRI involvement of bilateral pallidus, high excretion of urine sulfites and the missense mutation of the SUOX gene were important diagnostic clues for late-onset ISOD.