Abstarct: Free surface sloshing of liquid in a rectangular tank induced by lateral excitation with different heights of baffle in the middle of the tank and without it has been studied numerically and experimentally in this thesis. The numerical simulation is carried out baxsed on the volume of fluid (VOF) method that provides free surface extraction in such problem. Two tank with transparent walls, with baffle and without baffle, is used to free surface tracking in experimental study while the movement amplitude and frequency of periodic motion is controlled by a reciprocating designed mechanical system. This mechanical device provides a pure lateral periodic motion for liquid tank exciting. Free surface of sloshing liquid in rectangular tank obtained by image processing. Comparison of numerical results and similar experimental tests shows good agreement for different amplitude and different frequency of tank excitations in maximum and minimum of free surface displacement, so that relative errors estimated less than ten percent for all of tests. While they increase by increasing amplitude and frequency excitations due to nonlinear behavior of liquid free surface.