This study retrospectively investigated asparaginase-based chemotherapy treatment outcomes with or without radiotherapy in 143 patients with stage I-E-IIE extranodal natural killer/T cell lymphoma (ENKTCL). All patients received a median of three cycles of asparaginase-based chemotherapy, while 121 patients received radiotherapy following the chemotherapy. The complete remission (CR) rate for all patients post-chemotherapy was 58.7%, and rose to 73.4% by the end of treatment. Patients who received radiotherapy achieved better survival outcomes than those who did not (89.7% vs. 49.0% for 2-year overall survival (OS), P<0.001; 86.8% vs. 37.4% for 2-year progression-free survival (PFS),P<0.001). Additionally, even patients who achieved CR post-chemotherapy exhibited differential survival rates with or without radiotherapy (90.8% vs. 60% for 2-year OS, P=0.006; 86.1% vs. 60% for 2-year PFS, P=0.044). Multivariate analysis revealed that radiotherapy was an independent factor favoring OS (HR=0.098, 95% CI=0.031-0.314, P=0.001) and PFS (HR=0.156, 95% CI=0.062-0.396, P=0.001). Thus, radiotherapy is recommended for stage IE-IIE ENKTCL patients treated with asparaginase-based chemotherapy, even in cases of CR following chemotherapy.