Supercritical carbon dioxide (sc CO2) could greatly reduce the viscosity of heavy oils and consequently increases their fluidity on account of its special properties, whose density is close to that of the liquid while viscosity is similar to that of the gas. No matter if under reservoir conditions or in the pipelines, the fluidity of heavy-oil/sc CO2 is of major concern, especially for the process of CO2 injection development in deep heavy oil reservoirs and the transportation of heavy oil diluted by sc CO2. In this Article, a method to calculate viscosities of heavy-oil/CO2 mixtures is introduced, which is based on the Lederer equation. Contrary to earlier reports, this Article has calculated the parameters with empirical correlations especially for the viscosity of sc CO2, which was calculated with a computing procedure using equation of state in previous references. In addition, the viscosity of dead-heavy-oil at high-pressure and high-temperature (HPHT) and the volume factor, F-o, are also calculated using correlations, which were not proposed in former papers with correlations. The method could calculate the viscosity of heavy oil saturated with sc CO2 by inputting the least parameters including the density (or the specific gravity) and the viscosity temperature relationship of heavy oil as well as the pressure and temperature of the heavy-oil/sc CO2 system. With the proposed method of this Article, the viscosity of heavy oil saturated with sc CO2, could be obtained with reasonable accuracy after setting the given temperature and pressure. Experimental data of heavy oil saturated with sc CO2 at 70, 80, and 90 degrees C were regenerated with AARDs equal to 12.98%, 6.22%, and 2.43%, respectively. In addition, the AARDs of 70 degrees C were reduced from 12.98% to 9.73% with the leveling data.