The performance of asphalt concrete pavement depends on the bitumen properties, asphalt concrete mixtures volumetric properties and external factors such as traffic volume and environment. Bitumen is a visco-elastic material where temperature and rate of load application have a great influence on its behavior. Conventional bitumen is exposed to a wide range of loading and weather conditions; it is soft in a hot environment and brittle in cold weather. Higher traffic volume produces high stress within pavement layer, which is one of the main causes for pavement distress. Fatigue cracking and permanent deformation is considered as most serious distresses associated with flexible pavements. These distresses reduce the service life of the pavement and increase the maintenance cost. To reduce the pavement distresses there are different solutions such as adopting new mix design or by using asphalt additives. Using of asphalt additives in highway construction is known to give the conventional bitumen better engineering properties as well as it is helpful to extent the life span of asphalt concrete pavement. In this research an investigation was made on the fundamental studies of modified asphalt binder and mixtures in order to understand the influence of modifiers on the rheological properties and fatigue resistance with the aim of preventing fatigue cracking in asphalt pavement. The conventional bitumen (70/100) penetration grade was used in this research, modified with crumb rubber (CR) and styrene-butadiene-styrene (SBS) at four different modification levels namely 3%, 5%, 7% and 10% by weight of the bitumen. The rheological properties and fatigue resistance tests for asphalt binder were performed using a dynamic shear rheometer apparatus. Fatigue life for asphalt binder and mixtures were calculated based on the dissipated energy concept as well as a procedure for modifying of conventional bitumen was developed to find the suitable blending time and the optimum modifier content. From the results at low rubber content 3% and 5%, the behaviour of the modified bitumen remains close to that of the conventional bitumen and the optimum crumb rubber content for good rheological properties and long fatigue life was found to be 10% by the weight of bitumen. At higher (SBS) polymer content 7% and 10%, the behaviour of the modified binders remains close to that of the modified bitumen with 5% (SBS) and the optimum (SBS) content was found to be 5%. The fatigue behavior of modified bitumen was found to be significantly improved compared to conventional bitumen. Fatigue test using dynamic shear rheometer was found to be costly and time consuming. 3D finite element model for dynamic shear rheometer has been developed and was used for dissipated energy calculation. The experimental result and the model result showed excellent fit between dissipated energy for the same tested bitumen. On the other hand, a shift factor was found between the dissipated energy per volume from the bitumen specimen in dynamic shear rheometer and dissipated energy per volume for asphalt concrete mixtures in indirect tensile fatigue test.