This Thesis tries to explain why did Saudi Arabia conduct Proxy War to Iran in the Syrian Conflict. Since the beginning, Saudi Arabia and Iran had a stagnant relation; they are not far from confrontation. Their fight has always enlivened every conflict in the Middle East region, including the worst humanitarian problem in human history, which is the Syrian Conflict. Using Andrew Mumford’s proxy war theory and rational choice by focusing the approach on the rational actor model by Graham T.Allison, Saudi Arabia’s decision to take part in the Syrian Conflict through its proxies is based on the consideration of strategic outcomes and more rational cost-benefit calculations of proxy war.