This study investigates the construction of argumentation in journalistic discourse, using systemic-functional theory as the basis for the analysis of linguistic interpersonal resources (Halliday, 1994; Butt et al, 1995), as well as appraisal theory (Martin, 2000) and argumentation studies to identify the use of convincing and/or persuading strategies in opinion articles (Ducrot, 1983 apud Silva and Espíndola, 2005; Abreu, 2009). Qualitative research on this textual genre (Marcuschi, 2002) describes and interprets the use of lexico-grammatical aspects related to the Interpersonal Metafunction, aiming at a better understanding and evaluation of the effectiveness of texts. Positioning of the authors of the opinion articles is analyzed either through information management, which is related to the act of convincing, or through relationship management, which is related to the act of persuading. Nine opinion articles on varied themes and published during the year of 2010 in the newspapers O Globo and Folha de São Paulo were selected for analysis. Some of these articles were collected from the online version of the newspapers and others were taken from the printed version of the chosen news media. The study aimed at the selection, identification and analysis of the linguistic resources that realize modality and interpesonal grammatical metaphor, among other aspects; this phase of the analysis was followed by the semantic interpretation of the data. At the same time, in each text, the incidence of the act of convincing and/or persuading was examined, based on the attitudinal categories of affect, judgment or appreciation. Results of the research reveal that the act of convincing is quite recurrent in the argumentation of the analyzed opinion articles, showing that writers appeal to readers minds and ideas and they seek, in the own objectivity to the journalistic discourse, different ways to speak to the reason of their readership. On the other hand, the lexico-grammatical choices also show that several interpersonal resources are used in the texts with the intention of persuading and building a predisposition towards readers’ solidarity. At the same time, these linguistic choices allow for the expression of the writer s opinion in an indefinite or subtle way, making it difficult for readers to question, to refute or to disagree with the authors, who thus guarantee the success of their argumentation.