Abstract： Objective To investigate the value of DWI before treatment on predicting sensitivity of concurrent chemoradiation in nasopharyngeal carcinoma.Methods Seventy patients with nasopharyngeal carcinoma proved by nasopharyngoscope and biopsy pathology conducted DWI before concurrent chemoradiation and reexamined on receiving dose of 50 Gy.The mean, maximum and minimum ADC value of tumor were measured on DWI and maximum area of tumor before and during treatment ( on dose of 50 Gy) was delineated to calculate the tumor regression rate ( RS0-50 ).The patients were classified into three groups according to the RS0-50 as sensitive, moderate, and resistant therapeutic effect.Patients were classified into different groups according to the pathologic type and clinical stage respectively .Spearman correlation analysis was used between RS 0-50 and ADC values of all tumors , different pathologic types and clinical stages , respectively.ROC was used to evaluate the cutoff and value of ADC which had highest correlation to RS0-50 on predicting therapeutic effect.Results DWI of 3 patients were excluded due to obvious swallow artifact which influenced the measurement , and finally 67 patients were included in this study, with pathological type of nonkeratinized differentiated undifferentiated carcinoma in 49 cases, nonkeratinized undifferentiated carcinoma in 18 cases, clinical T1 stage in 7 cases, T2 in 14 cases, T3 in 17 cases and T4 in 29 cases.During treatment , there were 13 cases with sensitive therapeutic effect , 42 cases with moderate therapeutic effect and 12 cases with resistant therapeutic effect.RS0-50 [ ( 65.6 ± 3.1) %] showed mildly and moderately negative correlation to mean ADC [(1.06 ±0.19) ×10 -3 mm2/s] and maximum ADC [(1.29 ±0.33) ×10 -3 mm2/s] respectively ( r =-0.276, P =0.024 and r =-0.434, P=0.001, respectively).ROC showed when setting threshold at maximum ADC value of lower than 1.06 ×10 -3 mm2/s for predicting sensitive therapeutic effect , the specificity , sensitivity , and accuracy was 69.2%(9/13), 88.9%(48/54) and 85.1% (57/67), respectively, and when setting threshold at maximum ADC value of higher than and equal to 1.30 ×10 -3 mm2/s for predicting resistant therapeutic effect, the specificity, sensitivity, and accuracy was 75.0% (9/12), 65.5% (36/55) and 67.2%(45/67), respectively.Conclusion Pretreatment maximum ADC value were able to predict the tumor regression rate and sensitivity of concurrent chemoradiation in nasopharyngeal carcinoma .