We report on 4 children with invasive fungal infections complicated with leukemia who responded to voriconazole (VRCZ). In 3 children aged 1-6 years, the plasma VRCZ concentration was low and clinically ineffective after its administration at a dose of 4 mg/kg. Good plasma concentrations could be attained by increasing the dose to 5.3-12 mg/kg, and clinical effects were observed. In the other 13-year-old male, an adequate plasma concentration could be obtained after VRCZ administration at a dose of 4 mg/kg. Concerning adverse effects, transient visual abnormality developed in only 1 child. VRCZ may be effective and safe not only in adults but also in children with invasive fungal infection during chemotherapy for leukemia. Though the dose in adults is 3-4 mg/kg, the dose/weight in children should be higher because of the greater clearance. Since there are also individual differences in drug metabolism, the dose in children should be individually adjusted based on the plasma concentration.