The influence of some additives (Flexon processing oil, Struktol WE 16 slipping agent, and Struktol. MS 60 homogenizing resin) on state-of-mix, theological, tensile, and dynamic mechanical properties were investigated It; was found that extrudate swell of the rubber compounds with either processing oil or; NS 60 is governed mainly by the state-of-mix, but by wall slip in the case of compounds with WE: 16. As for the dynamic mechanical properties, the plasticizing effect is the major factor controlling the properties in the case of processing oil, while the degree of crosslink and dilution effect are the main factors in the case of NS 60. Both degree of crosslink and state-of-mix are responsible for the dynamic mechanical properties in the case of WB 16. In addition, it was, found that the tensile properties are controlled mainly by the plasticizing effect in the case of processing oil, but by the degree of crosslink in the cases of WB 16 and NS 60.