There is a growing recognition of the need for disaster management training for medical students in Saudi Arabia, but there is limited research on its effectiveness. Thus, this study evaluated the effectiveness of a disaster simulation training program for undergraduate medical students in Saudi Arabia. A disaster management simulation activity was conducted for 32 medical students. The students attended a 30-minute lecture about mass casualty incidents (MCIs) and completed a pre-simulation survey. They were then randomly assigned to one of three groups (performer, actor, observer) and asked to apply their skills to triage patients after a Level C MCI. A debriefing session was conducted using the plus/delta debriefing method. Then, the students completed a post-simulation survey. The results showed that after the simulation training the students' self-confidence in their ability to respond to a disaster increased from 40.7% to 59.4% (p value < 0.01), to utilize incident command structure increased from 37.9% to 62.5% (p value < 0.01), to demonstrate START triage for victims of a disaster increased from 28.2% to 65.7% (p value < 0.01), and to apply safe search and rescue techniques increased from 40.7% to 59.4% (p value < 0.01). The students' self-confidence in their ability to perform basic first aid skills also increased after the simulation. The study findings suggest that disaster management simulation training can be an effective way to increase medical students' self-confidence and preparedness for disaster response.