Purpose <p>Health-care professionals tend to delay advance care planning (ACP) discussions to prevent psychological distress and hopelessness among patients. However, the effects of ACP on hope, anxiety, ACP attitudes, and behavioral intentions in older adults with cancer remain poorly understood. Accordingly, this randomized controlled study explored the effect of ACP on hope, anxiety, ACP attitudes, and behavioral intentions in older adults with cancer.</p> Methods <p>Cancer patients aged &gt; 65&#xa0;years were recruited from a cancer center in northern Taiwan and screened using the Herth Hope Index (HHI), State-Trait Anxiety Inventory (STAI-S), Advance Care Planning Attitude Scale, and Behavioral Intention Scale. The experimental group participated in ACP conversations led by a trained nurse using a decision aid with cartoons; the control group received standard care. Data were collected at baseline and at 2&#xa0;weeks and 1&#xa0;month postintervention.</p> Results <p>We included 72 older adults. The two groups did not differ significantly at baseline. After the ACP intervention, HHI or Advance Care Planning Attitude Scale scores did not significantly differ by group, time, or group × time interaction. Furthermore, the STAI-S scores did not differ significantly between the groups, although the scores of both groups decreased significantly over time. The experimental group exhibited higher ACP Behavioral Intentions scores over time than the control group at baseline.</p> Conclusion <p>Health-care professionals should not use fear of patient hopelessness as an excuse to postpone ACP conversations. Future ACP interventions for older adults with cancer should focus on reducing psychological distress, presumably through cartoons.</p> Trial registration <p>Clinical trial registration number: NCT06061107 (2023–09-29).</p>