Galactosemia is a rare autosomal recessive disorder of galactose metabolism, which occurs as a consequence of a deficiency of one of these three enzymes: galactokinase, galactose-1-phosphate uridyltransferase, and uridine diphosphate galactose-4-epimerase, leading to elevated level of galactose and its metabolites in blood. The presented case was a 2-month-old, Thai female infant with persistent cholestatic jaundice, bilateral posterior subcapsular cataracts, and hepatomegaly. Laboratory investigations showed slightly elevated serum aminotransferase, and increased urinary excretion of galactose, galactitol and galactonate (by urine gas chromatography/mass spectrometry). These findings indicated an error in galactose metabolism. Soy-based formula was introduced to the patient. Clinical and laboratory results were improved after a few months of treatment. Genetic counseling was provided to the family for 25% of recurrence risk. Prenatal diagnosis is not established in Thailand.