This study presents laboratory experiments using surface Ground Penetrating Radar measurements to monitor hysteresis of the water retention function of a sand. A GPR system monitored the volumetric water content changes in a large sand column submitted to different hydraulic heads applied at its bottom during one cycle of drainage followed by imbibition. The average velocity of the electromagnetic waves measured during drainage was consistently smaller than the one measured at the same applied head during imbibition. This was attributed to the hysteresis of the sand water retention curve. Coupled hydrodynamic and electromagnetic modeling was used to simulate radargrams whereas hydrodynamic modeling coupled with 1D optical ray path was used to estimate the hydrodynamic parameters of the sand from GPR reflection two-way travel times. Statistical and uncertainty analysis were performed on numerical and experimental data. The range of optimized parameters were compared to those obtained with classical laboratory methods such as the hanging water column and the constant head permeameter.