This study was conducted to investigate the efficacy of pre-phase therapy in preventing tumor lysis syndrome (TLS) in cases with hightumor burden. This study involved 42 lymphoma patients with moderate to high risk of developing TLS. All of the cases underwenta prephase treatment which consisted of 1 mg of vincristine first day and 100 mg/day of prednisolone for seven days. Afterwards,planned conventional chemotherapy regimens were given. The development of laboratory TLS was evaluated by the end of the conventional cytotoxic treatment. Among the patients, 85.6% had B cell neoplasia and 14,4% had T cell lymphoblastic lymphoma (TCLL).The risk of TLS was high in 57.2% of the cases and intermediate in 42.8%. A total of 42.8% cases developed laboratory TLS afterconventional treatment following prephase therapy. On the other hand, there were 7.1% patients who exceeded the normal laboratoryvalue limits. In addition, 2.3% of the cases had only clinical findings of TLS. Treatment response was complete in 57.1% and partial in40.5% with respect to the findings of PET-CT. Prephase therapy may decrease the severity of TLS in cases with a high tumor burden.Prephase therapy may be used in the initial phase in cases at moderate-to-high risk for TLS