Introduction. Ascites of unknown origin in infants are rare and diagnostically challenging. However, it can be associated with a poor prognosis if it is not treated promptly. Case presentation. A 3-month-old boy infant was admitted to the Dr. Soetomo General Academic Hospital, Surabaya because of a 2-week history of progressive abdominal distension with massive ascites following fever onset. Laboratory parameter measurement revealed increased liver function test, hypoalbuminemia, and prolonged coagulation factor. Hepatitis markers were negative. TORCH serological examination showed non-reactive. Urinalysis, renal function test, and echocardiography were normal. The ascitic fluid analysis showed SAAG >1.1 g/dL. An abdominal ultrasound examination revealed ascites. MRCP showed hepatomegaly and ascites. A liver biopsy showed foci of polymorphonuclear and mononuclear inflammatory cell distribution among hepatocytes with no hepatic fibrosis. He was treated with antibiotics, steroids, diuretics, and albumin transfusion. There were no ascites and laboratory parameters were improved after treatment. Conclusion. Progressive and rapid hepatic inflammatory mechanisms may play a role in the development of ascites. Steroids may be considered in cases of unexplained ascites thought to be related to liver injury to prevent further liver fibrosis.