Viscosity is an important fluid transport property, and the viscosity data mostly are obtained from experimental measurements. The fixed path interference method with a cylindrical resonator is one of the most precise ways to gain the gaseous sound speed by measuring the resonance frequency and the half-width of the resonance peak. The gas viscosity affects the sound speed, leading to the offset of the resonance frequency and the increase of half-width of the resonance peak. Viscosity can be accurately acquired through the measurement of the resonance frequency and the half-width of the resonance peak, together with modifications due to the effect of the thermal boundary layer, the fill duct on the resonator shell, the transducer and the resonator shell vibration. In this paper, the way to acquire viscosity by the cylindrical resonator was developed and was verified by measuring argon (Ar) viscosity, and we find the result agreeing well with the data given in the literature.