Experimental results obtained in a gas-liquid bubbly flow in a flat horizontal sudden expansion are presented in this study and constitute useful data for the numerical code. The use of hot film anemometry in the continuous phase (liquid) of a bubbly flow allows a determination of the average and fluctuating velocity. For the dispersed phase, the use of a double optical probe allows the determination of the average and fluctuating axial velocity and the granulometry of the bubbles. A comparison of these quantities with the results obtained by a fast video camera shows very good agreement. The different measuring quantities were discussed and an organization scheme of the flow in a sudden expansion was proposed.