This study was initiated with the aim of evaluating the relative impact of different cross-linking agents on the rheological and morphological properties of polymer modified asphalt binders (PMAs). To complete this objective, two cross-linking agents (an aromatic oil and silicon oxide) were selected for evaluations. The cross-linking agents were then added to a styrene-butadiene-styrene (SBS) polymer modified binder (virgin PG 70-22) at different dosages. The selected cross-linking dosages were 2 and 4% by weight of virgin binder. The SBS, virgin binder, and cross-linking agents were mixed together for 90 minutes using a high shear mixer. The morphology of the modified binder was then tested using a florescent microscope and the rheological properties were evaluated using the dynamic shear rheometer (DSR) to determine the dynamic shear modulus values at different temperatures (i.e., 70oC and 76oC) and the multiple stress creep recovery (MSCR) properties of these binders.