A theoretical method is developed to investigate the coupled vibration characteristics of the ring-stiffened cylindrical shells partially filled with an inviscid, incompressible and irrotational fluid having a free surface. As the effect of free surface waves is taken into account in the analysis, the bulging and sloshing modes are studied. The Rayleigh-Ritz method is used to derive the frequency equation of the ring-stiffened and partially fluid-filled shells based on Love's thin shell theory. The solution for the velocity potential of fluid movement is assumed as a sum of two sets of linear combinations of suitable harmonic functions that satisfy Laplace equation and the relevant boundary conditions. The effect of fluid level, stiffener's number and position on the coupled vibration characteristics is investigated. To demonstrate the validity of present theoretical method, the published results are compared for simply supported shell and the finite element analysis is performed for unstiffened/stiffened, partially fluid-filled shells with clamped-free boundary condition.