The rheological behaviour in the molten state of Acrylo nitril– Butadine – Styrene (ABS) according to temperature, shearing stress and shearing rate have been studied. Measurements were made with a capillary viscosimeter for the static properties. The correction of experimental data has been carried out. Viscosity decreases with increasing shear stress or shear rate in the nonnewtonian flow high polymer systems. However, the variation of activation energy with temperature at fixed shear rate is always less then at fixed shear stress.