Background and Objective: Iran is a disaster-prone country and occurrence of disasters is inevitable. Early warning system is one of the most aspects in hospital preparedness. This research aim to determine the effect of early warning system on hospital readiness.

Material and Methods: This research was conducted in Motahari hospital in Tehran city, 2014. To perform early warning system based on the national program of readiness for disaster, we had frequent sessions with some health experts and the members of disaster committee. The level of   readiness was evaluated by WHO's checklist before.

Results: Following intervention, hospital preparedness rate increased by 25 scores demonstrating significant raise from moderate to high.

Conclusion: In regard with average level of readiness in Motahari hospital and its significant increase after using early warning system, we recommend applying this system for improving the level of hospital disaster preparedness.