In this paper, we investigate the impact of surprises made by scheduled monetary policy announcements on French stock market. Most of empirical studies achieved tends to test this effect on U.S stock market. Taken the French market as a representative European stock markets, we study the effect of both monetary policy signals from the ECB Council and the FOMC on the daily stock returns and volatility by using the standard event study methodology. We show that abnormal returns were observed few days before policy announcements. They coincide with the release of other macroeconomic announcements which produce uncertainty until the monetary policy announcement, that we show trigger a decrease on the volatility and a stabilizing effect.