In the present paper the influence of the carbon black quality parameter "fines content" was investigated with respect to the mixing process and the compound properties. It was found that the carbon black fines content influences the mixing process of the sulphur cured and EPDM based recipe to less extend. However, small variations of the specific mixing energy correlate with the macro-dispersion of the carbon black and the Mooney viscosity. In contrast to these results, the compression set, the die swell and the mechanical compound properties are significantly affected by the carbon black fines content, which can be explained by the existance of carbon black clusters. Furthermore, the cure rate of the compound is reduced by about 50% when the fines content increases, which is confirmed by variations of the sulphur dispersion.