Background: Radiation therapy (RT) plays an important role for pediatric cancer treatment strategies. The conventional RT can be used for effective tumor control in a short time, although the problem is that irradiation fields contain not only cancer lesion but also the surrounding normal tissue or organ. Intensity-modulated RT (IMRT) is a new method for tumor control with limitation of normal tissue exposure. The helical tomotherapy (HT), as Image-guided IMRT, was developed the rotational delivery of radiation in the manner of a CT scanner. We investigated effectiveness of tomotherapy, toxicity and tolerability during HT in nine treatments of seven children. Material and method: We retrospectively reviewed clinical data of patients with HT between January 2007 and May 20009. Patients were simulated by two series of CT scans, and computer plannings were performed during normal breathing. The planning target volume margins were about 1 cm. Tomotherapy was performed with compatible radiation dose according to tumor characteristics. Results: Seven children received nine events of tomotherapy. Their median age was 14 years old (7 ~ 18). The objective of HT was for palliation with disease control except a boy, who was for curative therapy. There was disease status in one boy with relapsed post-autoPBSCT neuroblastoma, relapsed rhabdomyosarcoma, one girl with relapsed Wilms tumor, two AML children with post-BMT chloroma, and two patients with nasopharyngeal cancers. Six of nine HT were not observed any adverse events during HT. A child with relapsed neuroblastoma experienced two times of grade II leucopenia and thrombocytopenia. Transient xerostomia controlled with steroid observed in a boy with nasopharyngeal cancer. All patients were showed good general performance status. There were alive in four children, who were two patients with stable disease, and two with complete response. Conclusion: The advantages of tomotherapy have increased homogeneity and conformity of dose delivery to tumor with low dose to adjacent risk organs. We proposed that HT might be a new strategy of RT in pediatric hemato-oncologic field. In addition, we need further evaluation of the possible long-term effects including secondary cancer, neurologic deficit or growth.