The pyrolysed oil shale (POS) obtained from the pyrolysis of bituminous rock was used as filler in poly(ethylene-co-vinyl alcohol) (EVAL). The effects of vinyl alcohol content in the EVAL and the particle size of pyrolysed oil shale in the mechanical properties were investigated. The EVAL was prepared by hydrolysis of poly(ethylene-co-vinyl acetate) (EVA) with 8 and 18 wt% of vinyl alcohol content. The composites were prepared in a rotor mixer at 180degreesC with concentration of pyrolysed oil shale up to 5 wt %. Stress-strain plots of compression-molded composites showed a synergic behavior in the mechanical properties for low concentrations (1-5 wt %) of POS in all particle sizes and EVAL used. Such behavior indicates a close packing and strong interactions between the inorganic filler and the polymer. Increasing of the vinyl alcohol content of EVAL improved the compatibility between the polymer and filler, but decreasing the POS particle size had no effect on the properties. The modulus and the ultimate tensile strength also increased in all concentrations of POS for both EVAL. Mechanical properties and dynamic mechanical analysis also demonstrated the compatibility between EVAL and POS. (C) 2004 Wiley Periodicals, Inc.