The effect of fluid viscosity on the vibration dispersion characteristics of an infinite circular cylindrical shell immersed in a viscous acoustic medium is studied. The Flügge’s thin shell theory for the isotropic, elastic and thin cylindrical shell, the wave equation for viscous flow field derived from the linear equations of continuity, Navier–Stokes and state and the appropriate wave-harmonic field expansions along with the pertinent boundary conditions are employed to get the equations of motion and the dispersion equation in the coupled system. Subse-quently, Numerical analysis is applied to solve the dispersion equation for the shell loaded with fluid at various viscosity coefficients. Then the dispersion characteristic curves, the Amplitude ratio curves of complex waves and the relative error parameter curves of non-dimensional axial wave number λ in the coupled system under different circumferential modals are displayed in several figures. It can be found from the figures that the influence of fluid viscosity on the dispersion characteristics of the propagating waves is more significant at low frequency range, while the variation tendency of the curves is nearly independent. As for the complex waves, the amount and cut-off frequency of the waves in the coupled system are proportional to the fluid viscosity coefficients.