Abstract: NPC patients 1 - 15 years after their radiotherapy which led to nab fibrosis in 40 patientswere analysed. When 60C0-γray or 8Mv X-ray was delivered, the incidence of fibrosis was only35. 1 %, 41. 6 %, respeCtively, while γ-ray combined with 120～ 140Kv X -ray or 10-14Mev β raygiven, the incidence rose to 83. 3%. The results shewed the most important cause of fibrosis was thetumor dose. When it was800cGY, only 27 of 70 patients (38. 6%) developed fibrosis, when≥8000cGY, 13 of 17 causes (76. 5 % ) mauifersed neck fibrosis, (P0. 01 ). Futher radioation shouldnot be given blindly after fairly high dose to neck nodes which were dsthated not to be eliminatedby radiotheray.