Estimating dynamic behavior of high-speed Planing vessels is one of the concerns of designers of such vessels. Evaluation of the loading and center of gravity variation effects, for small vessels with different motion modes, are very important at design stages. Such effects, if not taking into account correctly, may affect the final behavior of the vessel. In this research, for investigating the effects of loading and the center of gravity variations on the behavior of a monohull planing boat, a scaled- down 1:5 model was built based on the ITTC standard and Froude method. after the preparation and balance of the model, tests of the model have been carried out in the high-speed towing tank, in calm water and two loading conditions and at four positions of center of gravity. In each run of test (total 40 tests), the resistance, trim and sinkage, have been measured, and the longitudinal and transverse dynamic stability of the model has been qualitatively evaluated. The results show that increasing the weight will increase the resistance. increasing the distance of the center of gravity position from the stern, will reduce the resistance and trim in the displacement mode and increase the resistance in the planing mode. Also, the decreasing the center of gravity distance from the stern, will reduce the resistance and increase the trim in the planing mode, but may results in the longitudinal instability of the model in some extreme conditions.