The problem of infallibility is known as one of the most fundamental religious categories that affect religious epistemology considerably. Therefore, the notability of commentators` attempts in restudying the meaning of infallibility shows itself. Allameh Tabarsi one outstanding Imami commentator in his commentary has studied it from various aspects. The nature of infallibility, its field, its reasonability, the prophets, Imams and angles` infallibility are of the problems focused on here. Allameh, analyzing infallibility, has refuted the objections raised against the prophets` stories, solved the problem of infallibility on the basis of Quranic verses and studied the infallibility of consensus critically. Allameh`s methods of study include both fields of traditions and reasoning. He has proved the prophets` infallibility by reason and that of Imams with reliance on the Quranic verses. As shown in the paper, allameh has discussed the most notable problems in the field comprehensively