Background: Alagille syndrome (ALGS) is an autosomal dominant disorder that can affect the liver, heart, eyes, vertebrae, and face. ALGS is caused by mutations in the Notch signaling pathway members JAG1 or NOTCH2. The estimated prevalence of ALGS is 1 in 70,000 newborns. JAG1 gene mutations cause more than 90 percent of ALGS cases. This study aimed to determine the clinical, subclinical, and genetic mutation characteristics of ALGS in children in Vietnam. Materials and Methods: This cross-sectional study was conducted on all ALGS children treated in the Gastroenterology Department at Children’s Hospital No. 1 from September 2014 to September 2017. Results: Of the 30 enrolled ALGS cases, most patients that came from other provinces, were admitted to hospital mainly due to jaundice, and showed no significant differences in age or sex. The clinical features included 96.67% hepatic abnormalities, 80% spinal abnormalities, and 86.67% characteristic ALGS facial features. Subclinical features included significant increases in direct bilirubin and gamma-glutamyl transferase (GGT) levels. JAG1 mutations were found in 73.33% of the cases and included missense (32%), nonsense (36%), frameshift (23%), and splice site (9%) mutations. The most frequent mutation position was exon 4 (23.33%), with the remainder located throughout the JAG1 gene. Conclusion: Children with ALGS most frequently showed hepatic abnormalities, skeletal abnormalities, and characteristic facial features. Direct bilirubin and GGT indexes were strongly increased in all cases. JAG1 mutation was the main cause of ALGS. ALGS is novel in Vietnam, so more research is needed.