The objective of this study was to evaluate the rheological performance of rubberised asphalt binder with varying dosages of crumb rubber (CR), and compare these modified materials with unmodified asphalt binder. It is very important to investigate the characterization of chemical structures of the asphalt binder from a closer view for useful modifications of the virgin binder by polymer waste as modifiers. The current research employed a thin layer chromatography technique (TLC) to separate and determine the different fractions in asphalt. Nuclear Magnetic Resonance (NMR) spectroscopy was also used to characterize and confirm the chemical compositions of asphalt and its fractions. Despite of NMR spectra of asphalt is difficult to be interpreted via its structural complexity, but this technique is still able to provide useful data especially with regard to asphaltene fraction. Crumb rubber is a polymer waste which used as modifier of asphalt binder via the economic benefits and improving the rheological properties of modified asphalt binder. The rubberised asphalt binders were produced by blending the virgin asphalt with CR at various contents (3%, 5%, 10%, 15% and 20%). The effects of CR contents on the rheological behaviors of modified asphalt binder have been investigated including: penetration, softening point, ductility. Furthermore, morphological analysis of rubberised asphalt was conducted via scanning electron microscopy (SEM) to assess the effect of CR on the binder morphological structure. Based on results obtained, binder with highest CR content showed improvement in rheological properties of the modified binders in terms of decreasing in penetration, increasing in softening point values and keeping the ductility higher, unlike other CR contents which exhibited poor performance of modified asphalt.