SBS is a widely used polymer modifier for asphalt binders to improve the performance properties of hot mix asphalt. SBS is nearly indispensable when the binder properties do not satisfy the specification requirements under hot service temperatures. One of the concerns in using such additives, however, is the increased cost especially for large-sized construction projects. If a natural modifier can be used to replace some portion of industrial modifier products, such as SBS, it would significantly help reduce the cost of pavement construction. In this study, Gilsonite, a natural asphalt, is used as a binder modifier to reduce the SBS content based on a series of rheological testing. While studies on various properties of binder that is modified only by Gilsonite are common, we investigate the effect of combining SBS and Gilsonte in the same base binder. In the first phase, the binders modified individually with SBS and Gilsonite are evaluated in terms of based on the outcomes of dynamic shear rheometer and rotational viscosimeter tests. Then, the asphalt binders including both SBS and Gilsonite at different contents are subjected to the same rheological testing. The results show that around 3-4% times more Gilsonite is needed to replace 1% of SBS when the two modifiers are mixed in the same binder depending on the Gilsonite/SBS ratio selected. Besides, the viscosity of modified binders with a percent of SBS replaced with Gilsonite is always lower than that of SBS-only modified binder. It is suggested that Gilsonite can be used as an alternative modifier to reduce the cost of asphalt mixture production and compaction in the field. (C) 2011 Elsevier Ltd. All rights reserved.