While developing new polymers, a high level of stiff and simultaneously tough material behavior is an important goal. This study shows a new approach to optimize the stiffness/toughness behavior of polyamide 6 (PA 6) by incorporating both stiff and elastomeric nanofillers during melt compounding. For stiffness enhancement of PA 6, an organic-modified layered silicate (organoclay) was used, whereas to compensate for the toughness properties, a nanostructured PA 6/polyether block copolymer (PA 6-copo) was applied. In the first step, binary nanocomposites have been investigated whereby correlations between morphological and mechanical properties have been derived. Subsequently, these results have been used to adapt the processing conditions for the ternary nanocomposites. Despite a considerable interaction of both nanofillers the stiffness/toughness balance of the PA 6 nanocomposite has been optimized significantly. At a filler content of only 8 mass% organoclay and 8.3 mass% PA 6-copo, Young's modulus and tensile strength of PA 6 could be increased by 55% and 18%, respectively. In addition, the notched impact strength of PA 6 was enhanced substantially by 58%. POLYM. ENG. SCI., 54:247-254, 2014. (c) 2013 Society of Plastics Engineers