This report presents an experimental study investigating the dynamic pressure exerted on tank walls of ship by swashing internal fluid. As the first stage to the final object, the determination of the effectiveness of the members abating swashing fluid, the case, where no obstacle such as s wash-bulkhead and deep girder existed in the tank, has been dealt with. The model tank was 1 meter deep and 1 meter wide and the length was changed from 1. 4 meters to 3. 8 meters. Tests were carried out by putting the model tank on a specially designed rollig apparatus which is capable of simulating the pitching, surging and some other motions. The influencing factors, depth of fluid, tank length, amplitude and period of periodical motion of the tank and so on, were varied systematically. Total load, vertical variation of load and local pressure on the tank end wall was measured dynamically together with the motion of tank. The experimental results were regularized with regard to the tank motion. From this study, empirical formulae to predict the maximum load exerted on the tank end wall were derived as shown in Eq. (13) and Eq. (15) in the case of pitching and surging motions respectively.