Background: The aim of this study was to develop a tool to measure the family's difficulties in caring for cancer patients at the end of life at home: Family's Difficulty Scale in end-of-life home care (FDS). Methods: The draft of the FDS was derived from a pilot interview survey and literature reviews. The questionnaires were sent to 395 bereaved family caregivers whose family members were patients with terminal cancer receiving home service. Results: We obtained 306 responses (response rate, 81%). Factor analysis resulted in 29 items and 8 factors: Burden of Care, Concerns about Home Care Doctor, Balance of Work and Care, Patient's Pain and Condition, Concerns about Visiting Nurse, Concerns about Home Care Service, Relationship between Family Caregivers and their Families, and Funeral Preparations. The cumulative rate of contribution was 71.8%. Cronbach coefficient α for the FDS was 0.73-0.75; the intraclass correlation coefficient in the test-retest examination was 0.75-0.85. Evidence for construct validity was confirmed by convergent and divergent validity. Concurrent validity was confirmed by significant correlations between identified factors and concurrent measures. Conclusion: The validity and reliability of this new instrument were confirmed. This scale should help home care providers to assess and focus on family difficulties and provide individualized care for the family who cares for a patient with terminal cancer at home.