The objective of the study is the preparation and comprehensive characterization of novel high performance polylactide (PLA)-based composites designed with specific impact properties. Highly filled composites were obtained by melt-blending PLA and 40 wt % anhydrite II (AII) microfiller, the dehydrated form of calcium sulfate hemihydrate, a by-product having as origin the lactic acid (LA) fabrication process. The toughness of PLAAII composites was improved by addition of a selected impact modifier (IM) based on ethyleneacrylate copolymer (Biomax (R) Strong 100, noted BS). PLAAII composites containing (10 wt %) BS were prepared using two procedures: (1) the direct melt blending of all components in a single step and (2) the previously coating of AII by BS, followed by mixing of coated filler with PLA. These approaches were carried out to modify the phase structure and to determine their influence on the final composite properties. As reference samples, PLA and PLABS blends were accounted. The miscibility and phase morphology (differential scanning calorimetry and scanning electron microscopy), thermal stability (thermogravimetric analysis), and thermomechanical properties (DMTA, tensile, and impact tests) were investigated to explain the toughening mechanism in the BS-modified composites. Noticeable, an attractive threefold increase of impact strength with respect to the composite without modifier and remarkable thermomechanical performances were assessed. The composite obtained using BS-coated AII showed better properties (e.g., impact strength of 5.4 kJ/m2), improvements ascribed to the good filler dispersion and effective modification of interfacial regions (PLAfiller) by the BS-layer. (C) 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012