Pyrolyzed oil shale (POS) obtained from the pyrolysis of bituminous rock was burned in a normal atmosphere (POSB) to remove the organic phase and then used as a filler in poly(ethylene-co-vinyl alcohol) (EVAL). The effects of vinyl alcohol content, POSB particle size, and POSB concentration on the composite were investigated through measurement of mechanical properties. Composites were prepared in a rotor mixer at 180 degrees C. Stress-strain plots of compression-molded composites showed synergic behavior of the mechanical properties with low concentrations (1-5 wt %) of POSB, regardless of particle size or type of EVAL. Such behavior suggests close packing and strong interactions between inorganic filler and polymer, with the effects rein-forced by the mechanical properties. It was observed that the absence of the organic phase in the modified material improved the mechanical properties of the composites. Increasing the vinyl alcohol content improved the compatibility between polymer and filler in the EVAL/POS but did not affect the compatibility in EVAL/POSB composites. The relationship of mechanical and morphological behavior in the EVAL/POS and EVAL/POSB composites indicated that different factors were at play to explain the compatibility between the EVAL and the inorganic phase. (c) 2005 Wiley Periodicals, Inc.