Abstract： Objective To evaluate the treatment efficacy,toxicities and prognostic factors of nasopharyngeal carcinoma ( NPC ) treated with intensity modulated radiation oncology ( IMRT ).Methods Between January 2006 and August 2008,300 patients with pathologically diagnosed NPC from 6 center received IMRT.The number of patients with stage Ⅰ,Ⅱ,Ⅲ and Ⅳa+b disease (UICC/AJCC 2002 staging system) were 6,45,141 and 108,respectively.The prescription doses were as follows:70-74 Gy/30f toplanning target volume of primary nasopharynx tumor ( PTVRλ),68-70 Gy/30f to planning target volume of positive lymphnode (ptvnd),60-64 Gy/30f to higher risk region (PTV1),50-54 Gy/30f to lower risk region (PTV2).Patients with stage Ⅲ and Ⅳa+b disease also received cisplatin-based chemotherapy.Cox method was used for Multivariate analysis.Results The follow-up rate was 99.7％.The 4-year rate of local control,regional control,metastasis-free survival (DMFS),disease-free survival (DFS) and overall survival (OS) was 94.0％,95.5％,87.4％,80.8％,86.1％,respectively.Mucositis was the most severe acute toxicity,with 18.0％ grade 1,48.7％ grade 2,33.3％ grade 3.No patient suffered from grade 4mucositis.Xerostomia was the most common late toxicity,with 12.0％ grade 0,75.7％ grade 1,12.3％grade 2.No grade 3-4 xerostomia was observed.There were 18,15 and 42 patients failed in local,regional and distant metastasis,respectively.Multivariate analysis showed that N stage was the only prognostic factor for OS (x2 =5.17,P=0.023),DMFS (x2 =6.91,P=0.009) and DFS (x2 =8.15,P=0.004) in these patients.Conclusions IMRT can improve the treatment efficacy of NPC.The acute and late toxicities were tolerated.Distant metastasis becomes the main treatment failure.N stage is a significant prognostic factors.