Nanoscaled Al2O3 powder is used as additive in coarse-grained Al2O3 green bodies. Its influence on the green density is investigated. The potential effect of powder mixing on the green density is described by a model for multimodal powder mixtures that predicts the powder composition for maximum green body density. The model is applied to bimodal and trimodal mixtures with one of the components being nanopowder. The calculated relative densities are compared with experimental results. Furthermore, sintering experiments are conducted to investigate the influence of the amount of nanoscaled powder on the sintered densities of bimodal bodies.