Background: Currently concomitant or sequential chemotherapy with radiotherapy has been recognized as the standard treatment for extranodal natural killer/T-cell lymphoma, nasal type (ENKTL). However, the optimal schedule has not been fully defined. Methods: We designed a phase II prospective study to investigate the efficacy and toxicity profile of sequential radiation followed by systemic GDP (gemcitabine, dexamethasone and cisplatin) chemotherapy on previously untreated early-staged (stage IE/IIE) ENKTL patients with at least one unfavorable prognostic factor. The primary endpoint was 2-year progression-free survival (PFS). Secondary endpoints were 2-year overall survival (OS), overall response rate (ORR), and toxicity. Results: A total of40 patients were enrolled and completed the entire course of treatment between June 2010 and June 2014. The median age was 38 (range 25-63) years old. All the enrolled patients presented with at least one unfavorable prognostic feature: age > 60 years (5.0%), B symptom (40%), elevated serum LDH (40.0%), regional lymph node involvement (32.5%) and primary tumor invasion (87.5%). At the completion of the whole treatment, ORR was 97.5% and the complete remission rate was 95.0%. Median follow-up time was 43.7 months (range 9.4-72.3 months). 2-, 3-, 5-year PFS rates were 84.7%, 82.1%, 77.5%, and OS rates were 89.9%, 87.1%, 79.7%, respectively. Recurrence within the RT field was observed in four patients and systemic failure in three individuals. Grade 1-2 skin reaction and mucositis were the main toxicity related to radiation. Grade 3-4 neutropenia (12/40), thrombocytopenia (7/40) and anemia (2/40) were observed during GDP chemotherapy. No clinically significant late toxicities were observed during follow-up visits. Conclusions: The current results indicates that first-line radiation followed by GDP chemotherapy can be one of the most effective and feasible treatment schedule for early-stage ENKTL patients, especially those with poor prognostic factors. Clinical trial information: NCT02276248