In this research, fly ash was modified with oleic and stearic acid and PVC/DOP/fly ash composite was prepared by melt - mixing process. The relative melt viscosity, tensile properties, flame retardancy as well as structure morphology of the PVC/DOP/modified fly ash composite was investigated. In the presence of modified fly ash, the processing ability and the tensile properties of PVC/DOP are enhanced in comparison with using unmodified fly ash. Additionally, the modification process also improves the dispersibility of fly ash into PVC/DOP matrix, which was observed in FESEM images. Otherwise, the flame retardancy of all tested samples reached maximum level according to UL-94 standard.