Although gallbladder (GB) hydrops in childhood is uncommon, it is most commonly associated with Kawasaki disease (KD) and can be a risk factor of poor outcomes in patients with KD. Our patient presented with a fever, diffuse abdominal pain, maculopapular rash, bilateral conjunctivitis, red and fissured lip tissue, and 3 days of right cervical swelling. Abdominal examination revealed abdominal distension and tenderness. Abdominal ultrasonography was performed to identify the source of abdominal symptoms, which revealed dilatation of the GB. Abdominal computed tomography scan was also performed to exclude other hepatobiliary disease, which showed normal hepatobiliary systems. The GB of our patients returned to a normal size without any complications, but it regressed very slowly. We report a case of a 6-year-old boy with KD who presented with markedly distended and unusually prolonged GB hydrops.