The objective of the monography is to investigate the factors thatexplain the projection of the image of middle power of Brazil s presidencialdiplomacy for Mercosur in the period of the first mandate of Luís Inácio Lulada Silva. The hypotesis that is intended to be confirmed lays that there was atransformation of the socialcultural structure of the international system, thatpointed to the consolidation of the open regionalism and to the majorparticipation of the countries in multilateral and sub-regional foruns. Suchtransformation led to a redefinition of the brazilian identity and this State triedto reinforce its credentials to the position of global player, in special, with thedefense of democratic principles in the regional level and liberal values in themajor political foruns.With this redefinition, the interests of the country in theprojection of an image of middle power were enhanced, specialy in relation toits regional partners, since Mercosur would permit to Brazil, in the economiclevel, the ampliation of the competitivity of brazilian industry and theconsolidation of its bargain power in the hemisferic level and in thenegotiations with the EU, and, in the political level, the creation of a stableneighborhood and the previsibility of the behavior of its partners.