Alagille syndrome (ALGS) is an autosomal-dominant multisystem disorder caused by mutations in Jagged 1 (JAG1) or NOTCH2. The penetrance is low but highly variable. It is almost exclusively diagnosed in children with cholestasis and, more rarely, in their adult relatives. Here, we report the case of a patient diagnosed with ALGS in adulthood. The patient was a 28-year-old male who presented with characteristic facial features, an eye abnormality, chronic cholestasis with bile duct paucity on liver biopsy, atrial defects and stenosis of the left internal carotid artery. A novel frameshift mutation, c.2087_2088insAAAAATGG (p.W697Kfs*49), in JAG1 was identified. To our knowledge, this is the first case of ALGS diagnosed in adulthood in China. ALGS should be considered as a differential diagnosis for intrahepatic cholestasis in adult patients with a wide variety of clinical manifestations, including cardiac disease, skeletal abnormalities, ocular abnormalities and characteristic facial features.