Experimental and theoretical approaches were employed to analyze the static and dynamic mechanical properties of acrylonitrile butadiene styrene (ABS) nanocomposites reinforced with multiwalled carbon nanotube (MWCNT) and nanosilica. Enhanced stiffness and tensile strength were observed for composites with 5% (wt) CNT and 3% (wt) nanosilica. Micromechanical models were highly promising to predict the experimental Young's modulus by 2% (wt) of nanofiller content, beyond which it deviated due to the nanofiller population and the reduction in interparticle distance. At the optimum content of 5% (wt) MWCNTs in the ABS matrix, enhanced storage and loss moduli and lowered damping peak were observed, which was attributed to the immobilization of the segmental polymer chains. From the DMA parameters, the dynamics of the polymer chain were investigated and the fraction of constrained regions and entanglement density were quantified. These findings demonstrated that composite with higher constrained regions and entanglements exhibited superior mechanical performance. Amongst all composites, 5% (wt) MWCNT-reinforced ABS composite showed an increment in reinforcing efficiency, entanglement density, and constrained regions by 195.6%, 115% and 55.5%, respectively, with regard to 3% (wt) nanosilica-reinforced ABS composite. The effectiveness of dispersion and interfacial adhesion of CNTs with ABS was improved by carboxyl treatment and functionalization with ABS-g-MaH compatibilizer with regard to silane-treated nanosilica/ABS composites. Combined analysis of microstructure, tensile properties and dynamic mechanical parameters such as entanglement density, effectiveness of filler, constrained volume of polymer chains and adhesion factor demonstrated the effectiveness of high aspect ratio carboxyl-treated MWCNTs as a better reinforcing agent in comparison with nanosilica in ABS matrix.