In recent years the use of inflatable dams has become more widespread throughout the world. Various people have done studies on the shape and membrane tension of these structures; however, only a few authors have considered dynamic behavior. Due to the nature of the applications and the material composition of these structures, a study considering the dynamic response of an inflatable dam is warranted. In this study, the equation of motion for an air-inflated dam is derived, then solved using the Galerkin approximation method. The solution is performed for a one-term approximation and a two-term approximation, where both solutions use a sine function to approximate the deflected shape of the dam. Frequencies and amplitudes are calculated and presented in tables and plots for the first four modes, and three different values of the central angle of the dam. Comparisons to the results of other studies are presented at the conclusion of this study. / Master of Science