Polymer/carbon nanotube (CNT) composites are one of the most perspective advanced materials developed in recent years. The properties of CNT-reinforced polymer composites, however, strongly depend on structural aspects of the nanostructured filler and on its dispersion quality in a polymer matrix. Consequently, this research was devoted to the investigation of multiwalled-CNT-modified poly(vinyl acetate) (PVAc) composites with respect to the mechanical property dependence on some structural characteristics of CNTs. PVAc/CNT nanocomposites were obtained with a solution casting technique. The amount of CNTs was changed from 0.01 up to 2 wt %. The stress-strain characteristics of PVAc/CNT nanocomposites clearly revealed remarkable reinforcing effects of the CNT additions already at 0.01 wt %. At this CNT concentration, the elastic modulus (E) and tensile yield stress increased by 12.5 and 60%, respectively. Special attention was paid to the change of E with respect to some structural characteristics of CNTs. A corresponding mathematical model for the prediction of the elastic properties of CNT polymer nanocomposites is proposed, showing that elastic constants of the nanocomposites largely depend on the agglomeration of CNTs. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 122: 3569-3573, 2011