<b><i>Objectives:</i></b> Long-term clinical follow-up and mutation analysis were performed in 27 Chinese congenital hyperinsulinism patients. <b><i>Method:</i></b> 27 hypoglycemia patients were diagnosed with CHI within 2 years of age. The long-term clinical outcome was analyzed and mutation analysis of 5 hyperinsulinism candidate genes was performed. <b><i>Results:</i></b> The median onset age of hypoglycemia in the patients was 60 days; 11 patients showed hypoglycemic symptoms in the neonatal stage, and hypoglycemia in most of the patients was first expressed as a seizure. Blood was collected during the hypoglycemic episode and insulin levels were significantly elevated. <i>ABCC8</i>,<i> KCNJ11</i>, <i>GCK</i>, <i>HNF4a</i> and <i>GLUD1</i> genes were screened for mutation analysis. 14 mutations in <i>ABCC8</i> or <i>KCNJ11 </i>genes in 12 cases were identified (44%). 57% (8/14) of the mutations have not been reported before. 83% (10/12) of the patients have a monoallelic mutation. 58% of these 12 patients were predicted to be focal. 73% of the patients without KATP channel mutations were sensitive to diazoxide. 26 patients were followed over a period of 1-13 years. 50% of all 27 patients showed brain impairment. <b><i>Conclusions:</i></b> Chinese CHI patients are similar to other ethnic groups in terms of prevalence of KATP-HI, onset age, severity of hypoglycemia and treatment. Mutations in <i>ABCC8</i> and <i>KCNJ11</i> are common causes of CHI in Chinese patients. Mutation analysis showed more novel and monoallele mutations in KATP genes.