This study analyzes the effect of credit rating announcements on stock returns in the Brazilian market during 1997-2011. We conducted an event study using a sample of 242 observations of listed companies, 179 from Standard and Poor's and 63 from Moody's, to analyze stock market reaction. Abnormal returns have been computed using the Market Model and CAPM for three windows: three days (-1, +1), 11 days (-5, +5) and 21 days (-10, +10). We find statistically significant abnormal returns in days -1

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... and 0 for all the three types of rating announcement tested: initial rating, downgrades and upgrades. For downgrades, consisted with prior studies, our results also showed negative abnormal returns for all practically all windows tested. Overall, our findings evidence the rating announcements do have information content, as it impacts stock returns causing abnormal returns, especially when they bring 'bad news' to the market.