Abstract : The speed of sound in cavitating flows varies signifi cantly according to the local void fraction. Actually, it is close to 1500 mis in pure water, 400 m/s in the vapor, and it may decrease drastically in the liquid-vapour mixture. This implies that cavitating flows are nearly incompressible in areas of pure liquid, and highly compressible in two-phase flow regions. Taking into account the compressibility of the flow in numerical simulations is necessary to reproduce some campIex mechanisms associated with cavitation instabilities. This requires a correct estimation of the local speed of sound in a cavitating medium. The principal objective of this thesis was the creation of a homogeneous cavitating area in order to measure the speed of sound inside. So an experimental device was developed to create such an area. Two methods are investi gated for measurement of the speed of sound : I - with 3 equidi stant pressure transducers along the test section II- with 2 hydrophones located face to face in a cross test section. The void fraction is measured with an optical probe. The calibration of the optical probe and the validation of transducers and hydrophones measu rements, are performed in air-water flow. The method I, which is found to be more appropriate for the measurement of the speed of sound, is applied for a cavitating flow. For both flow configurations (air-water and cavitation), the results are compared with existing theoretical models and discussed. A nice agreement is obtained between the experiments and the theory.