Background: Combined modality therapy (CMT), namely chemotherapy combined with radiotherapy, has been recommended for patients with localized extranodal natural killer/T-cell lymphoma (ENKTL). However, the optimal CMT has not been fully clarified. As chemotherapy is more easily accessible than immediate radiotherapy in the routine clinical practice, the “chemotherapy-first” CMT including sequential or sandwiched radiotherapy deserves further exploration. In addition, the optimal non-anthracycline-based regimen needs to be confirmed. Methods: The P-GEMOX regimen was administrated as follows: pegaspargase 2000 IU/m2 intramuscular on day 1, gemcitabine 1000 mg/m2 intravenous on day 1 and 8, oxaliplatin 130 mg/m2 intravenous on day 1 and was repeated every 21 days. Patients who achieved at least stable disease (SD) subsequently underwent involved field radiotherapy (IFRT). The dose of IFRT ranged from 50 to 55 Gy. Performing sequential radiotherapy (4 cycles of CT+RT) or sandwich radiotherapy (2 cycles of CT+RT+2 cycles of CT) is determined by the clinician based on the patients' conditions. The primary endpoint was the overall response rate (ORR) after 2 cycles of chemotherapy, and secondary study endpoints were CR, PFS, and OS. Safety was also evaluated. Results: From August 2020 to April 2023, thirty-seven patients (23 men, 14 women; median age: 55, 26-76 years) with stage I/II ENKTL who had received P-GEMOX were collected. 14 patients were stage IE and 23 were IIE. ALL patients completed at least 2 cycles of P-GEMOX, which resulted in 94.6% (35/37) of ORR including 30 patients with CR and 5 patients with PR. Among the patients in remission, 15 patients received sequential radiotherapy, 15 received sandwich radiotherapy, 4 were waiting for or in the process of radiotherapy, and 1 patient progressed before radiotherapy. With a median follow-up of 14.8 months (range: 2.6-38.1 months), the 3-year PFS and OS were 87.2% (95%CI 69.3%-95%) and 90.6% (95%CI 72%-97.1%), respectively. Sandwich radiotherapy had an obvious trend for longer PFS than sequential radiotherapy (18moths-PFS 100% vs. 78%; P=0.073). During the treatment, 21.6% (8/37) of the patients experienced grade 3–4 treatment-emergent adverse events (TEAEs). The most grade 3–4 hematological TEAEs were neutropenia (7/37, 18.9%) and thrombocytopenia (4/37, 10.8%). As for grade 3–4 non-hematological TEAEs, elevated aminotransferase, hyperbilirubinemia and hypofibrinogenemia were 16.2%, 10.8% and 8.1%, respectively. The adverse events of this CMT were well-tolerated and manageable. No treatment-related death occurred. Conclusions: Our study demonstrated that CMT consisted of P-GEMOX showed favorable efficacy with acceptable toxicity, and sandwich radiotherapy (CT+RT+CT) seems give more favorable PFS than sequential radiotherapy. The CMT protocol could be an effective treatment option for early-stage ENKTL patients.