This article aims at contributing to study the stock market's reaction up to the point of generating significant abnormal returns or cumulative abnormal returns within the Brazilian impeachment period. By means of the efficient market hypothesis (EMH), in its semi-strong form, the purpose was verifying whether the presidential impeachment that took place in Brazil in 2016, in 3 different dates, brought the expected reaction from the stock market on the Brazilian Stocks, Commodities and Futures Exchange (BM&FBOVESPA). The theme is relevant, as it addresses aspects of politics and economic theory and their interactions in stock markets. It impacts in the area of capital markets, because this suggests that economic players can, through their expectations and information, see adverse reactions in the market. The methodology analytically employed encompasses a brief literature review as a theoretical basis about the institutions involved and it refers historically to impeachment events. Quantitatively, the methodology consists in the study of events, so that the expectations are observed by means of time-series regression models based on the autoregressive-moving-average (ARMA) models. The result found, under three major events that culminated in the 2016 Brazilian presidential impeachment, was that no significant statistics has been determined, at a 5% level, in all estimated windows and in all events. Statistically, it was not possible to reject the hypothesis that the abnormal returns and the cumulative abnormal returns equal zero. So, the markets have been considered to be well-informed regarding the events, in this specific situation, i.e. according to the EMH, in its semi-strong form, the markets have reacted as expected.