Defense and security is a most important issue which enjoys a specific status in social and political studies, including Imam Khomeini who, among the outstanding thinkers, has produced statements and views, and set out to explain the concept and function of security and defense by covering subjects on Kalam (science of discourse) and Figh (Islamic jurisprudence). Most of Imam Khomeini's viewpoints on this field can be observed in his arguments put forward on political Figh. From Imam Khomeini's viewpoint, security in personal domain is directly intermingled with security in social domain, and are supplementary. In other words, personal security, which is a function of peoples' feelings, equals social security in its collective form. Off course, continued public life is the same as social and social life, in that people's security and the society's security form a continuity. When security, both in personal and social terms, faces different dangers and threats, the issue of defense is put forward. The present article tries discuss the issue of security and defense in relation with guarding the foundations of the Islamic Republic of Iran as viewed by Imam Khomeini, using the descriptive-content analysis method. The related information has been collected using the library and digital method. In the next stage, it begins to analyze Imam Khomeini's viewpoints in relation to defense and security relying on the data discussed above. One can state, from Imam Khomeini's statements, that defense is considered as a philosophical and realistic mechanism, which means repelling enemy and providing effective deterrence supplies, and constitutes as a critical and foundational rule. It follows that thinking, as viewed by Islam's foundations of defense thought, is deemed to be among the primary preparations for formulating the affairs related with the Islamic society and providing security. In other stages the way optimal solutions can be found on the issue of defense becomes important.