We report a case of hemophilic pseudotumor in the ulna of a 6-year-old boy treated with radiation therapy. A total dose of 900 cGy in 6 fractions was given in 6 consecutive days. Progression of cystic changes was halted within a month. New bone formation and trabeculation were found on the 4th month. Complete healing of the lesion and bony replacement were found on the 12th month. The patient was followed up to 72 months and there was no evidence of recurrence and no bone growth disturbance. Radiation therapy can be an effective alternative modality in treating hemophilic pseudotumor.