Isovaleric acidemia (IVA), a recessive autosomal disorder, is caused by isovaleryl-CoA dehydrogenase deficiency. Isovaleric acidemia may present with symptoms during the acute stage of severe metabolic acidosis, ketosis, vomiting and altered mental status. This report concerns a 2-month-old female infant diagnosed as isovaleric acidemia by tandem mass spectrometry. She presented with two episodes of vomiting, poor activity and pancytopenia without obvious metabolic acidosis and hyperammonemia. She received combined therapy of L-carnitine, glycine and low protein and leucine diet. Hemogram and serum isovalerylcarnitine (IVC) were measured during the treatment. The depressed leukocyte and platelets recovered when serum isovalerylcarnitine level increased.