A new model of single cavitation bubble dynamics has been developed to include the effect of bulk liquid viscosity in addition to the effects of evaporation/condensation of water vapor, thermal conduction and the compressibility of a liquid. In this study, the liquid viscosity is divided into two parts: viscosity at the bubble interface (μ′) and viscosity of the bulk liquid (μ). A set of numerical calculations with and without μ has been completed under different viscosities (0.001–0.014 Pa s) to quantitatively analyze the effect of μ on single cavitation bubble dynamics. The results show that the effect can be negligible for small viscosities, but it should be taken into account for relatively high viscosities.