Purpose: The purpose of this study was to examine the knowledge, caregiving performance, stress levels, and mental health of family caregivers of terminal cancer patients with delirium, insofar as these characteristics are relevant for delirium. Methods: Between May 1, 2019, and June 1, 2020, 96 family caregivers of terminal cancer patients with delirium completed a structured survey, the results of which were analyzed. Results: The average correct answer rate for delirium-related knowledge was 53.2% across all subcategories, which included knowledge of causes (41.5%), symptoms (65.4%), and caregiving (51.7%). The average score for family caregivers' performance of caregiving for delirium was 2.60 ±0.5, with subcategories including caregiving for patients without delirium (2.16±0.95), caregiving for patients with delirium (2.84±1.01), and stress related to caregiving for delirium (39.88±16.55), as well as categories such as patient-related caregiving (44.32±28.98), duty-related caregiving (44.21±30.15), and interpersonal relationship-related caregiving (22.35±25.03). For mental health, the average score among family caregivers was 1.96± 0.70, with the highest score being for the category of additional items (2.28±0.84). Family caregivers of patients with hyperactive delirium as the delirium subtype had higher scores for caregiving performance than caregivers of patients with mixed delirium. Conclusion: Scores for the delirium-related knowledge and caregiving performance of family caregivers were low, while their caregiving stress levels were high due to their lack of knowledge and experience. This indicates the importance of delirium-related education for family members of patients with delirium and the necessity of developing nursing intervention programs to help manage stress and promote mental health among family caregivers.