The temperature dependences of the dynamic viscosity of InBi_{100 –х}Pb_х melts (where х = 19, 40, 60, 80, 100 at. %) in the range from the liquidus temperature to 1200 K are studied by the method of damped torsional oscillations. The temperature dependence of the viscosity of investigated melts is well described by the Arrhenius equation. The viscosity of InBi–Pb melts at a constant temperature has small negative deviations from the viscosity of an ideal mixture. The activation energy of a viscous flow has negative deviations from additive values with a minimum near 20 at. % lead. The concentration dependence of the viscosity of the melts of this system was calculated using well-known equations based on data on thermodynamic properties. The results obtained are compared with experimental data.