This work deals with the characterisation of the linear viscoelastic properties, closely related to its performance as road paving binder, of ambient ground tire rubber-modified bitumen. Specifically, 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 that shown by unmodified and polymer-modified (SBS) bitumens. In total, an unmodified bitumen, five ground tire rubber-modified and three polymer-modified (SBS) bitumens have been studied. Rubber-modified bitumens show improved viscoelastic characteristics and, therefore, higher viscosity than unmodified binders. Consequently, enhanced resistance to permanent deformation or rutting and low-temperature cracking should be expected in ground tire rubber-modified bitumens. In addition, rubber-modified bitumen (9 wt.%) shows very similar linear viscoelastic properties to SBS-modified bitumen having 3 wt.% SBS at -10degreesC, and 7 wt.% SBS at 75degreesC.