Background <p>Patient aggression is a persistent challenge in mental health settings, and undergraduate preparation in de-escalation remains variable. This study evaluated whether a standardized-patient (SP) de-escalation simulation improves psychological empowerment and confidence in coping with aggression among psychiatric nursing students.</p> Methods <p>We conducted a parallel-group randomized controlled trial (pretest–posttest) with undergraduate psychiatric nursing students randomly assigned to either an SP-based de-escalation simulation program or routine curriculum control. The intervention comprised 12 sessions over 8 weeks (4 theory + 8 SP practical scenarios with structured debriefs aligned to INACSL standards). Primary outcomes were psychological empowerment and confidence in coping with patient aggression, assessed at baseline and immediately post-intervention using validated scales. Fidelity was supported through scripted scenarios, SP calibration, and facilitator adherence/debrief quality checks. Between-group differences in change scores were examined.</p> Results <p>Compared with the control group, students in the simulation arm demonstrated significantly greater gains in both psychological empowerment and confidence in coping with aggression from pretest to posttest. Fidelity indices indicated consistent SP portrayal and facilitator adherence across sessions, and attendance was high. No adverse events were reported.</p> Conclusions <p>A structured de-escalation simulation using trained standardized patients significantly improves empowerment and confidence among psychiatric nursing students. The scenario maps, learning outcomes, and debriefing approach described support replication and curriculum integration in undergraduate mental health nursing. Future work should examine longer-term retention, transfer to clinical practice, and curriculum-level outcomes.</p> Clinical trial number <p>Not applicable.</p>