The aim of this work is to characterize the velocity field of water inside a partially filled cylinder subjected to a harmonic excitation and to use the obtained results to validate numerical simulation performed in OpenFoam. Fluorescent 2D Particle Image Velocimetry (f-PIV) has been applied to characterize the velocity field in the plane in which the external excitation is applied. PIV results are compared to numerical. The results from this work can be used to better understand the effect of the sloshing motion on structures and to have basic information for the design of baffles. The facility is composed by a unidirectional sloshing table, a cylindrical cell, designed and manufactured in order to minimize image distortion, and PIV system. Neutrally buoyant fluorescent particles are used to seed the flow. The measurements are carried out in “phase locked mode”, i.e. the image acquisition is synchronized with a specified phase of the external harmonic motion on-line by an Optical Displacement Sensor (ODS).