Objective　To investigate the pathogenesis, clinical manifestations and genetic characteristics of hyperinsulinism-hyperammonemia (HI/HA) syndrome caused by GLUD1 gene mutation. Method　Clinical data of a case with HI/HA syndrome was retrospectively analyzed, and relevant literature was reviewed. Results　The girl began to have repeated hypoglycemia since she was 1 year and nine months old. During the course of more than two years, convulsions had happened for 3 times which was recovered by elevated blood sugar and anticonvulsant therapy each time. Laboratory data showed that the level of blood insulin and ammonia was elevated, which was defined as HI/HA syndrome. High-throughput sequencing analysis revealed a de novo heterogeneous missense mutation (c.965G > A, p.Arg322His) in GLUD1 gene. Conclusion　Gene detection could confirm the diagnosis of HI/HA syndrome.