Viscosity measurements in combination with pulsed magnetic fields are developed by use of a quartz-crystal microbalance (QCM). When the QCM is immersed in liquid, the resonant frequency, f₀, and the quality factor, Q, of the QCM change depending on (ρη)^0.5, where ρ is the mass density and η the viscosity. During the magnetic-field pulse, f₀ and Q of the QCM are simultaneously measured by a ringdown technique. The typical resolution of (ρη)^0.5 is 0.5%. As a benchmark, the viscosity of liquid oxygen is measured up to 55 T.