The influence of melt-compounding technique on blast furnace slags (BFS) filled polystyrene (PS) compounds was investigated. BFS are byproducts of iron industry, and are formed during the production of iron via thermo-chemical reduction in blast furnaces. BFS are mineral-structured materials composed of severeal such as silicon oxide (SiO2), calcium oxide (CaO), magnesium oxide (MgO) and alumina (Al2O3) as well as other minor oxides and elements. Such combination of oxides might be of technical advantage if BFS is properly prepared and tailored for use as a functional filler for PS. In addition, BFS is outstandingly inexpensive and require minimal refining costs compared to common mineral fillers used in polymer industry such as calcium carbonate and talc, giving BFS an economic significance. In current study, compounds were produced via melt-compounding approach, where two different processing technologies were used: (1) Laboratory rotor-blade internal mixer (IM) and (2) co-rotating, twin-screw compounding extruder (TSC). It was found that compounding process did not yield a strong influence on the rheological properties, where comparable levels for shear viscosity, storage- and loss moduli were observed for all compounds except for ‘20G40 TSC’ compound. Such deviancy was clear in thermal properties of this particular compound, where slightly lower transition temperature (Tg) as well as higher specific heat capacity (Cp) were reported. For mechanical behavior, comparable stress-strain curves and young’s modulus values for both processes were witnessed. Deviant ‘20G40 TSC’ compound showed slightly lower young’s modulus compared to corresponding IM.