Objective To evaluate the validity and reliability of the Chinese version of Xerostomia Questionnaire ( XQ-C) in nasopharyngeal carcinoma patients treated with radiotherapy. Methods XQ-C was translated according to the International Quality of Life Assessment project approach. Patients with nasopharyngeal carcinoma in different radiotherapy stages were enrolled in this study and assessed by using the XQ-C. The validity and reliability of the questionnaire results were evaluated. The content validity was assessed by experts grading method. The construct validity was assessed by exploratory factor analysis. The discriminant validity was determined by non-parametric method. The reliability was evaluated by Cronbach′s α and split-half reliability to assess the internal consistency. Results A total of 212 questionnaires were completely filled out. Content validity showed that the item content validity index ( I-CVI) ≥0.80, Scale-CVI/Ave=0.97, and P value of Kendall′s W test was 0.701. Exploratory factor analysis revealed that XQ-C was a unidimensional scale. The scale scores of patients at different stages of radiotherapy significantly differed, suggesting that the discriminant validity was good. Cronbach′s α of the scale was 0.951 and Guttman′s semi-reliability coefficient was 0.940. Conclusion The XQ-C is valid and reliable, which can be widely applied in the clinical diagnosis, treatment and research of xerostomia in Chinese nasopharyngeal carcinoma patients after radiotherapy.