Objective: To clarify factors related to emotional instability in spouses of cancer patients receiving palliative chemotherapy. Methods: Semi-structured interviews were conducted with spouses of cancer patients receiving palliative chemotherapy, and the obtained data were qualitatively and inductively analyzed. Results: Through analysis, 9 related factors were identified: “realizing the severity of the situation when receiving an explanation of the pathological condition”, “an unclear prognosis”, “fear of losing any treatments”, “being pressed for treatment-related decision-making”, “increased daily burdens by the care”, “collapse the visions of the family future”, “communication with medical professionals”,“candid dialogues with the patient”, and “relationships with others”. Conclusion: It may be important for nurses to help families of cancer patients realistically manage their situation without excessive confusion, even when they experience emotional instability, and spend meaningful time with patients as an outcome of treatment, with an understanding of these related factors on such emotional instability.