In this study, an alternative filling material, fly ash was tested in PVC pastisols. Therefore, - 38 .m Soma fly ash sample was used and its results were compared with that of calcite material as a filler. Therefore, this study was conducted to have three sections as: 1) Characterization of powders calcite, fly ash and PVC powder: SEM, XRF, XRD, Size measurement, 2) Preparation and characterization of PVC plastisols with and without fly ash: Rheological measurements 3) Characterization of final PVC product: Surface, hardness and strength tests. The results of fly ash were always compared with the results of calcite and discussed in this thesis. It was suggested that fly ash could be an alternative filling material for PVC plastisols. It.s effect, on the other hand, was found to change depending on the temperature, mixing speed and concentration. In overall, the mechanical properties of PVC-product obtained were affected positively and better PVC materials were obtained. Under some conditions, however, the rheological properties were became shear thickening while it was newtonian and shear thining before. The changes in the rheological properties of PVC plastisols and the mechanical properties (quality) of final PVC-product were all explained by the differences in the composition and shape of the fly ash particles. Because, the composition and shape of the particles are expected to affect the interactions of PVC particles with that of filler material which will definetely affect the quality of material.