This research work has evaluated the modification effects of adding the reactive polymer (poly methyl methacrylate - (PMMA)) at different contents with Iraqi asphalt in the presence of poly phosphoric acid (PPA) at constant ratio as cross-linking agent on the thermal and rheological behavior of asphalt material with penetration grade 40/50. Moreover, the chemical structure of Iraqi asphalt and its fractions (asphaltene and maltene) was analysed using FTIR analysis. Combination of PMMA/PPA with asphalt has been presented as a new alternative approach to modify the rheological and thermal behavior of modified asphalt binders via forming chemical bonds and the changing in rheological and thermal characteristics of blended materials. Ten different PMMA percentages ranging from 0.5% to 5% by weight with 0.2% PPA for each sample were blended with 40/50 asphalt binder, the rheological properties of modified asphalt samples at different contents were examined by standard testing including ductility, penetration, softening point and penetration index. It was noted that due the addition of high loadings of PMMA into asphalt, the softening point value increased from 51 ˚C to 66 ˚C, whereas the ductility and penetration values decreased from 150 cm and 41 mm to 33 cm and 12 mm respectively. The result obtained revealed that the incorporation of PMMA/PPA with asphalt at specific level significantly improved elasticity and strengthens of asphalt mixture, which finally enhances the cracking and rutting resistance performance as well as temperature susceptibility of asphalt pavement. The thermo gravimetric analysis (TGA) indicated that the modified asphalt samples had less evaporation and higher thermal stability compared to virgin asphalt, this means that the thermal attitude of modified asphalt was improved. X-ray diffraction (XRD) patterns were performed to study the morphological properties of asphalt and modified one, these results showed that modified asphalt sample possessed homogeneous surface as a result of uniform dispersion of polymers into asphalt morphology due to chemical interaction between polymers and asphalt.