A writer/politician uses his personal or his group ideology along with a special goal in producing a political text.This ideology can be extracted by recognition of disavowal discourse policy in which, at first, something positive is presented and then rejected by a special term like” but”, and is used for self-legitimation and other-delegitimation. Micro-structure of the texts of the western editorials about Iran’s nuclear activity, with disavowal method, represents the legitimation of this activity and America’s domination on it, in its own way. Therfore, this paper, by a critical approach, has studied the function of disavowal in the Wall Street Journal and Washington Post from America and the Guardian, the Independent from Britain in 2009 in order to answer this question that how the western newspapers have represented the legitimation of Iran’s nuclear activity from America`s view. The results show that America’s view on Iran’s nuclear activity is unipolar and exclusive and the western newspapers have mostly used disavowal approach, in theoretical justification and rational representation, to legitimize this attitude.