Different theories of international relations have different views into rationality of international relations actors. The theories influenced by the positivism approach, especially neorealism, consider governments as rational actors, in the sense that they seek to advance their preferences in such a way as to maximize their interests. Rationality in this approach takes place Based on the calculation of material profit and loss in competition with others. in return, for post-positivists and Islam, this definition of rationality is incorrect and limited, because they consider the role of ideological, normative and socialization factors of actors to be involved in their rational behavior. The current research aims to investigate rationality in positivist, post-positivist and Islamic theories, has raised this question: What criteria do positivist, post-positivist and Islam theories consider for the rationality and rational behavior of actors in the field of international relations? The hypothesis is that the calculation of material profit and loss is the criterion of positivist rationality, but norm-oriented and value-oriented rationality is the criterion of the rationality of actors' behavior in post-positivism, and logical rationality, which is the calculation of both material profit and loss and spiritual values, is the criterion of the rational behavior of actors in Islam. Considering that how theories are processed in the form of meta-theory, in order to investigate rationality, the ontological, epistemological and methodological metatheoretical foundations of theories are discussed. The present research has come to the conclusion with descriptive-analytical method that although instrumental rationality is a useful analytical concept to explain some important motivations of international relations actors, but the rational behaviors of the actors in some cases are guided by strong ideological, moral or emotional motives.