Abstract： Objective To determine the diagnostic value of diffusion weighted imaging(DWI) for primary nasopharyngeal carcinoma(NPC) and metastatic lymph nodes,and to establish the diagnostic thresh-old of apparent diffusion coefficients(ADCs). Methods Conventional MR scans and DWI scans were con-tinuously performed in 56 patients with newly diagnosed NPC and 55 healthy volunteers. All patients re-ceived primary tumor biopsy and MR image-guided cervical lymph node fine-needle biopsy. ADC and eADC values of both primary lesions and lymph nodes were calculated and compared. Results According to the pathological diagnosis,all the 56 patients had non-keratinizing carcinoma and 51 had lymph node metastasis. In the control group,75 cervical lymph nodes were found. ADC values of both primary NPC and metastatic lymph nodes were significantly lower, while eADC values were higher than those of normal controls. Setting the ADC value threshold at 0.809 ×10-3 mm2/s, the sensitivity and specificity for primary NPC detection were 80.4% and 74.5%, respectively. The negative and positive predictive values were 79.2% and 77.6% ,respectively. The accuracy was 78.4%. Setting the ADC value threshold at 0. 708×10-3 mm2/s, the sensitivity and specificity in the detection of metastatic cervical lymph nodes were 43.1% and 93.3%, respectively. The negative and positive predictive values were 70.7% and 81.5% ,respectively. The accura-cy was 73.0%. Conclusions DWI might be a new diagnostic approach in the detection of primary NPC as well as metastatic lymph nodes.