The chaotic motion of a fully simply supported plate with large deflection subjected to subsonic flow and transverse periodical uniform load is studied. The equation of motion of the subsonic plate with large deflection is established using von Karman’s large deflection theory and Hamilton’s principle. The Lyapunov exponent method is used to determine the threshold value of the flow velocity for the plate’s motion being from periodic to chaotic. Four-order Runge-Kutta method is used to solve the equation of motion. The bifurcation diagram, displacement-time history, phase portrait and poincar? map are computed and compared with the results obtained by the Lyapunov exponent method. From the results, it is shown that the Lyapunov exponent method is an effective method in estimating the threshold value of the flow velocity for the chaotic motion of the system. When the flow velocity exceeds the threshold value, the dynamic characteristics of the plate is from periodic motion to chaotic one.