Since radiation was considered as a major therapeutic modalities, chronic ulceration on lumbosacral area has been eventually generated. When the lumbosacral soft tissue defect cannot be closed with a local flap, the option of a free flap should be considered. Vascularized muscle flap is a good choice on the radiation ulcer due to chronic infection and the tissue changes of radiation effects. From October 1998 to March 2001, six patients of radiation ulcer was received microvascular transfer of five free latissimus dorsi muscle flaps and one latissimus dorsi myocutaneous flap using the superior gluteal vessel as a recipient. Patients' age ranged from 45 to 74 (mean 63.3 years of age). Mean follow-up period was 19.7months (1 to 43 months). All the flaps survived with complete recovery. One case of skin graft loss was completely healed without any further intervention. In conclusion, free muscle flap with hyperbaric oxygen therapy could be successfully applied for the treatment of radiation ulcer on lumbosacral area. It can be concluded that free muscle flap transfer with hyperbaric oxygen therapy can be a preferable therapeutic modality for radiation ulcer in lumbosacral area.