BackgroundStudies have indicated that the advance care planning knowledge and attitudes of elderly individuals strongly affect their implementation of advance care planning. A measurement with a theoretical base for evaluating elderly individuals’ knowledge, attitudes, and behavioral intentions regarding advance care planning is lacking.ObjectivesTo develop a questionnaire and understand elderly individuals’ knowledge, attitudes, and behavioral intentions regarding implementing advance care planning.MethodsA cross-sectional questionnaire survey was conducted. The content validity index, and statistical methods, including discrimination, factor, and reliability analysis, were adopted for psychometric testing. Descriptive statistics mainly presented data analysis.Results401 elderly individuals were recruited from a medical center and one senior activity center. The content validity index was approximately 0.71–0.92 for the developed questionnaires, the Kuder–Richardson formula 20 was 0.84 for advance care planning knowledge, and the Cronbach’s alpha was 0.86, 0.94, 0.76, and 0.92 for attitudes, behavioral intentions, influencing factors, and subjective norms, respectively. The average score for advance care planning knowledge for elderly individuals was 4.42, with a correct answer rate of 49.1%. They lacked knowledge of advance care planning-related legislation. The mean score for attitudes and behavioral intentions was 14.32 and 3.48, respectively. Elderly individuals agreed that advance care planning has benefits but were worried about the emotional distress caused by advance care planning discussions. Elderly individuals with positive behavioral intentions tend to implement advance care planning. Spouses, children, doctors, and nurses are significant reference people for elderly individuals.ConclusionsThe developed questionnaire exhibits good validity and reliability for understanding elderly individuals’ knowledge, attitudes, and behavioral intentions concerning advance care planning. Advance care planning materials or decision aids suitable for elderly individuals must be developed to increase their understanding of advance care planning. Additionally, the role of nurses is indispensable in promoting advance care planning among elderly individuals.