Abstract： Objective To analyze the dose distributions of changing target volumes during intensity modulated radiotherapy (IMRT) for nasopharyngeal carcinoma (NPC). Methods Twenty-one NPC patients received definitive IMRT. A total of 126 computed tomography (CT) planning images were acquired, including the first CT scan for the primary plan and a series of scans taken weekly from the start of treatment to the fifth week. The images were registered to the planning images. Target volumes (GTV_(nx), CTV_1 ,CTV_2 ,PTV, and PTV_2) and normal structures (the parotid, brain stem and spinal cord) were re-contoured on the fusion CT images. Results The D_(mean) D_(95), D_(90), D_(10), D_5 and V_(100) of GTV_(nx) were 15.44 -15.60 Gy (F=0.07,P=0.996),14.66 -14.92 Gy (F=0. 11,P=0.990),14.81 -15.06 Gy (F= 0. 12,P=0.988),15.88 -16.29 Gy (F =0.28,P=0.924),16.00 -16.38 Gy (F=0.25,P =0. 940) and 98. 1% -99. 5 % (F = 0. 08, P = 0. 995), CTV_1 with 14. 75 -14. 98 Gy (F = 0. 07,P = 0. 997), 13.39 -13.73 Gy (F=0.20,P=0.964),13.74 -13.96 Gy (F=0.08,P=0.995), 15.65 -15.90 Gy (F= 0.09,P=0.994),15.91 -16.05 Gy (F=0. 10,P=0.992), 98.2% -99.5% (F=0.02,P= 1.000), and CTV_2 with 13.34 -13.64 Gy (F=0. 18,P=0.970),12.71 -13. 18 Gy (F=0.32,P=0.898), 12.89 -13.28Gy(F=0.23,P=0. 949) ,13.79 -14.03Gy(F=0. 12,P=0. 987) ,13.92 -14. 16 Gy (F=0. 12,P=0.987), 94.4% -99.6% (F=0.25,P=0.937), respectively. Conclusions No significantly different dose distributions exists with the changes of the target volumes, even on the largest variations of external contours. The primary plan could ensure adequate doses to the changing target volumes. The replanning is unnecessary in terms of the change of target volumes during radiotherapy.