Subsequent to an allogenic stem cell transplantation(ASCT) on patients with hematologic malignancy(AML, ALL, CML, multiple myeloma, lymphoma etc.), chronic GVHD(graft versus host disease), which is an immunological reaction, occurs. With treatment results from patients who were diagnosed with ALL(acute lymphocytic leukemia), undergone BMT(bone marrow transplantation) and showed oral and skin lesions due to GVHD, treatment of oral manifestations of leukemia and its general management were studied. 90% of patients with chronic GVHD show change in the oral mucosa causing oral manifestations such as leukoplakia, lichenoid change of the oral mucosa, mucosal atrophy, erythema, ulceration and xerostomia. In treating GVHD, extensive systemic immunosuppression cause bacterial, viral, fungal infection that are fatal, and even if the treatment is successful, the patient is already in a severe immunosuppressed state. Therefore, localized target therapy is preferred. In another words, topical application(rinse, cream, ointment etc.) of cyclosporin and steroid in treating oral chronic GVHD is highly recommended, and the use of PUVA(Psoralen Ultraviolet A) and thalidomide is reported to be effective. In treating such diseases, dental treatment to control pain and prevent secondary infection of oral manifestations is very important. To those patients with systemic diseases who show limited effect by general dental treatment, non-invasive treatment such as the dental laser, in addition to the use of drugs, may be necessary to actively treat pain and help the healing process. For greater results, new effective methods are to be developed for treatment.