ENKTL is a rare and highly aggressive disease. Due to the rarity, most published studies evaluating new treatment regimen for ENKTL enrolled approximately 20-40 patients in their studies. Since the phase I of this study is designed as 3+3 dose escalation, then this study will enroll approximately 3-12 patients with localized stage in phase I for dose finding. The beginning dose of brentuximab vedotin will be 1.2 mg/kg, escalating gradually until dose limiting toxicity (DLT) is observed. Initially, 3 patients will be treated with 1.2 mg/kg of brentuximab vedotin and will be monitored for DLT. If there is no DLT observed in all 3 patients at the end of their first treatment cycle, dose escalation to the next dose level (1.8mg/kg) may commence. If there is a DLT observed in 1 of the first 3 patients, additional 3 patients will be included, expanding the cohort to 6 patients. This cohort of patients will be treated with the same previous dose of 1.2 mg/kg and monitor for DLTs. If no DLT observed, dose escalation to the next level (1.8 mg/kg) may commence. If there are DLTs observed in 2 or higher in any of the 6 patients prior dose (0.8mg/kg) will be defined as MTD. There will be no further additional patient inclusion and dose escalation beyond the maximum number of 12 patients and 1.8mg/kg, as MTD will be exceeded.