International boundaries have been one of the preoccupations of Political Geography since their appearances. The shape and type of boundaries are an important issue in national security and for the offensive or defensive position of countries. Studies have been done and more attention has been paid to the boundaries geometry (convex, concave, directness) in recent decades. Also this study wants to verify the impacts of boundaries geometry on national security. This descriptive and analytical article studies the impact of western boundaries geometry of Iran on national security. Results of research show that concave boundaries play a defensive role and convex boundaries play an offensive one. thus the convex boundaries have significant security sensitivity and attract more human, economic and military resources to preserve their security in order to guarantee the national security.