Present work is devoted to the study of the tensile behavior of polypropylene (PP)/mica composites with improved interfacial interactions from the matrix side caused by the presence of a p-phenylen-bismaleamic acid grafted atactic polypropylene (aPP-pPBM) as an interfacial agent. Hence, aPP-pPBM was previously obtained, in our laboratories, by reactive processing in the melt of a by-product (atactic PP) from industrial polymerization reactors. Present article is two-fold, on one hand it has been planned to evidence the so called interfacial effects caused by this novel interfacial agent (aPP-pPBM) yielding better final properties of the heterogeneous system as a whole as revealed by tensile mechanical properties, and on the other to obtain models to forecast the overall behavior of the system. For such purpose, a Box-Wilson experimental design considering the amount of mica particles and of interfacial agent as independent variables was used to obtain polynomials to forecast the behavior of the PP/Mica system in the experimental space scanned. The existence of a critical amount of aPP-pPBM to optimize mechanical properties appears to emerge. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 113: 3929-3943, 2009