The increase of the interest in polymer nanocomposites has been leading to continuous growing search toward nanofillers alternative to the widely known clay-based ones. One of these possible alternatives is represented by calcium carbonate nanoparticles, which have not been widely investigated in such context. In this article, a study on the rheological and morphological behavior of different low density polyethylene-calcium carbonate nanocomposites, compared with a reference calcium carbonate microcomposite, is presented. Several different nanosized calcium carbonates at different amounts were used. The results from the rheological and mechanical tests outlined that only minor changes occur when the amount is up to 2 wt %. The use of higher filler concentrations or the increase in the processing time can significantly affect this behavior. SEM analysis allowed deeper understanding of these phenomena. (C) 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 127: 2544-2552, 2013