The paper analyses the relationship between the power blocs and regional integration policies of the Brazilian and Chilean States. We are interested in understanding how the interests of dominant classes and class fractions influence regional integration projects in South America, such as Mercosur and the Pacific Alliance. Our hypothesis is based on the characterization of bourgeois fractions in peripheral social formations in relation to foreign capital, developed by Nicos Poulantzas. In Chile the hegemonic fraction within the power bloc is the comprador bourgeoisie - fraction dependent principally on the international market - and in Brazil, the fraction which had occupied important position until 2014 is the interior bourgeoisie - fraction that is dependent on foreign capital in terms of finance and technology, but it depends on the domestic and the regional markets. Therefore, the regional integration project of the Chilean state is open regionalism, while Mercosur is a multidimensional integration project (fragile and unfinished).