Nurses play an important role in maintaining patients' dignity. How to measure patients' dignity and dignity-related distress is an important issue in nursing care. Use of a reliable and valid tool assessing dignity-related distress in patients is necessary. The study investigated the validity and reliability of the Mandarin Version of the Patient Dignity Inventory (PDI-MV) in cancer patients. The Patient Dignity Inventory (PDI) was translated into the Mandarin language using forward and back translation. A convenience sample of 125 adult cancer patients was recruited from the oncology ward of a medical center in southern Taiwan. Factor analysis with principal axis factoring extraction method and oblique rotation (promax) was used to assess the construct validity. Concurrent validity was established using the Patient Health Questionnaire-9 (PHQ-9), Mandarin version of Demoralization Scale (DS-MV) and the Rosenberg Self-Esteem Scale (RSES). Internal consistency was used to examine the reliability. Data were collected from February to May 2016. As a result of the factor analysis, four factors, including existential distress, loss of support and sense of meaning, symptom distress, and loss of autonomy. Concurrent validity showed that the PDI-MV was significantly correlated with the PHQ-9 (r = 0.25-0.54), DS-MV (r = 0.30-0.58) and the RSES (r = - 0.08 to-0.30), Cronbach's alpha coefficients for the PDI-MV and four factors were 0.95, 0.95, 0.84, 0.83, and 0.89 respectively. The PDI-MV is a psychometrically sound instrument assessing a broad range of dignity-related distress issues in cancer patients.