The principal aim of the present study was to clarify what kind of assessments are performed by nurses practicing delirium care for terminal cancer patients. We conducted semi-structured interviews twice with six certified nurse specialists in cancer nursing/certified nurses in palliative care. Furthermore we analyzed the results using qualitative content analysis techniques. Our results revealed that nurses performed risk assessments to prevent delirium based on “understanding risk of developing delirium based on both intuition and knowledge,” performed assessments based on “examination of information necessary for early detection based on the risk of onset of delirium” and “determination of whether emerging symptoms are delirium” to determine the presence of delirium, and understood the aspects of delirium and experiences of delirium patients through “exploring factors already appearing in delirium,” “understanding the overall picture of delirium performed after determination of delirium,” and “significance of symptom experience of delirium.” These findings suggest how educational intervention should follow the stages of this assessment in order to improve the quality of delirium care for terminal cancer patients.