Gilbert's syndrome is a benign, often familial condition characterized by asymptomatic jaundice. A patient suffering from Gilbert's syndrome may have hepatic activity of bilirubin-UDP-glucuronosyltransferase decreasing to levels around 30% of the normal. A clinical diagnosis of Gilbert's syndrome is usually followed in case of mild hyperbilirubinemia with a high fraction of unconjugated bilirubin, normal values of liver enzymes, and no overt signs of hemolysis. This article reported a 17-year-old male with only partial indication of indirect hyperbilirubinemia. Rifampicin test and caloric restriction test were applied to assure the patient had Gilbert's syndrome. These two non-invasive diagnostic means, with the benefit of avoiding hazardous liver biopsy, are gaining popularity in our routine Gilbert's syndrome examination.