One of issues that are predicted in criminal law to protect the individuals’ right is legal self-defense. It entered in criminal laws of most countries around the world and is also recognized in UK. Self-defense is the most important example of permitted crime that is eroded the legal part of crime. So, when the conditions of self-defense exist, the defendant act shall not be considered as crime. But it is permissible that the defender is done and base on that, not only has no criminal liability but also has no civil liability. England, like Iranian legal system, recognizes self-defense and in certain situations and circumstances and considers the use of force and legal violence. In legal system of England, like Iranian one, self-defense is recognized and in certain situations and circumstances, it considers the use of force and violence as a permissible measure. In justifying its philosophy, different comments and theories have been proposed and base of self-defense is expressed by these views. The controversial issue of self-defense isn't limited to criminal law of Iran. All legal systems allow their followers in term of serious violations of their rights or others, if is necessary even by force, to protect themselves or others. In various legal systems, there are different approaches to range and subject of belligerency. Therefore, in this paper, a comparative study about aggression in defense issues in Iran and England is performed and theoretical foundations of criminal law in these countries are presented. In This type of detailed comparative study of legal systems, the useful results and conclusions are presented; so many ambiguities in the legal system are cleared.