End-of-life discussion with patients with advanced cancer is one of the important factors to determine the patient quality of life and their families' grief. The primary aim of this study is to collect Japanese medical oncologists' views toward end-of-life discussion. A context analysis of free comments of the questionnaire survey was conducted. Questionnaires were mailed to 864 medical oncologists, and 490 responses were obtained. A content analysis identified 420 free comments. As barriers of end-of-life discussion for oncologists, three types of barriers were emerged: 1) issues relating to patient and family (e.g., [individuality of the patient and family], [difficulty of acceptance of illness progression]), 2) issues relating to medical professionals (e.g., [a lack of psychological support], [difference in beliefs about end-of-life discussion among medical professionals]), and 3) health care systems (e.g., [a lack of time and human resources], [a lack of education and research]). The findings of this study may be useful to improve mutual understanding of oncologists and palliative care physicians when performing the end-of-life discussion in collaboration.