As to the treatment of soft tissue tumor in children, we have performed intraarterial infusion chemotherapy in 3 children, two of whom had rhabdomyosarcoma and one of whom had infantile fibrosarcoma, at Sapporo National Hospital. The former two patients had large and unresectable solid tumor. In the latter case, an uncommon disease of childhood, local excision was considered while sacrificing a significant degree of function in the affected part. We describe here these three cases and the effectiveness of this therapy. Intraarterial chemotherapy reduced the tumor remarkably and facilitated second-look surgery. Although transient hematuria, slight articular contracture and vasculitis were observed in each case as side effects during the therapy, they were only minimal and tolerable. Unfortunately, one patient relapsed 6 months after surgery, but two patients are still in good health without recurrence. According to the results of our study, we believe that this method can be effective for controlling unresectable primary malignant soft tissue tumor.