Background: The Western individualistic understanding of autonomy for advance care planning is considered not to reflect the Asian family-centered approach in medical decision-making. The study aim is to compare preferences on timing for advance care planning initiatives and life-sustaining treatment withdrawal between terminally-ill cancer patients and their family caregivers in Taiwan. Methods: A prospective study using questionnaire survey was conducted with both terminally-ill cancer patient and their family caregiver dyads independently in inpatient and outpatient palliative care settings in a tertiary hospital in Northern Taiwan. Self-reported questionnaire using clinical scenario of incurable lung cancer was employed. Descriptive analysis was used for data analysis. Results: Fifty-four patients and family dyads were recruited from 1 August 2019 to 15 January 2020. Nearly 80% of patients and caregivers agreed that advance care planning should be conducted when the patient was at a non-frail stage of disease. Patients' frail stage of disease was considered the indicator for life-sustaining treatments withdrawal except for nutrition and fluid supplements, antibiotics or blood transfusions. Patient dyads considered that advance care planning discussions were meaningful without arousing emotional distress. Conclusion: Patient dyads' preferences on the timing of initiating advance care planning and life-sustaining treatments withdrawal were found to be consistent. Taiwanese people's medical decision-making is heavily influenced by cultural characteristics including relational autonomy and filial piety. The findings could inform the clinical practice and policy in the wider Asia-Pacific region.