This work deals with the characterisation of the linear viscoelastic properties, closely related to the performance as road paving binder, of ambient ground tire rubber-modified bitumen. With this aim the influence that rubber particle size exerts on the rheological properties of these binders has been studied. The resulting viscoelastic behaviour has been compared with those shown by unmodified and polymer-modified (SBS) bitumens. Thus, unmodified bitumen, three ground tire rubber-modified and three polymer-modified (SBS) bitumens have been studied. From the experimental results obtained we may conclude that rubber-modified bitumen shows enhanced elasticity in a wide range of the mechanical spectrum of the binder. Thus, a modified bitumen containing 9% ground tire rubber shows similar linear viscoelastic properties to those found in a modified bitumen containing 3% SBS.