Social advertising, understood as a type of discourse, is characterized by the use of different persuasive strategies that are adopted on a regular basis for the construction of such discourse.The paper aims to present an analysis of some social advertisements where contrast is used as an expression strategy for the construction of persuasive discourse. The research was carried out from the analysis of 4 advertisements selected for their use of contrast as a persuasive strategy. In the advertisements analyzed, contrast appears in both verbal and nonverbal signs, that is, in the text and in the image. Based on such analysis, contrasting concepts are identified and placed in semiotic squares to perform the analysis. Results show that in this type of advertising there is an exhortative macro-act, consisting of two subparts, a request speech act and a commissive speech act, which is structured in a cause-consequence relationship. The structure of the commission act creates a threat and functions as an argument of the request speech act.