Effects of silica particles with different nature (Hydrophilic and Hydrophobic) on PP/PS (80/20) blends were investigated using rheological properties. The hydrophilic fumed silica used in this study was AEROSIL OX50 and the hydrophobic one were SIPERNAT D17 and AEROSIL R202. All ingredients were simultaneously mixed in Haake internal mixer at 200 ˚C and 50 rpm for 8 mins. Large Amplitude Oscillatory Shear (LAOS) tests were carried out at frequency of 1 rad/s to probe nonlinear rheological properties and linear rheological properties were measured using Small Amplitude Oscillatory Shear (SAOS) tests. All the rheological measurements were conducted at 180˚C and under oxygen atmosphere. The Nonlinear-Linear viscoelastic Ratio (NLR ≡ Normalized nonlinear viscoelasticity /Normalized linear viscoelasticity) was used to quantify the degree of dispersion and distinguish the different responses of silica particles with different nature. SEM images revealed that Hydrophilic OX50 silica could not improve morphological properties of the blends. On the other hand, hydrophobic silicas (R202 and D17) both improved morphological properties. It was found by TEM images that OX50 silica aggregated inside PS droplets and made PS phase more difficult to breakup into smaller sizes. D17 and R202 both improved rheological and morphological properties regardless of the droplet size reduction mechanisms. Interestingly, NLR parameter could estimate the morphological behavior of the blends by showing increments (NLR>1) for hydrophobic silicas and constant values for hydrophilic silica (NLR≅ 1) (Inverse correlation between NLR and droplet size evolutions). However, NLR values for the PP/PS/R202 blends were relatively larger than those of PP/PS/D17 with lower droplet sizes. This is, particle-particle (dispersion) effect is more dominant factor in NLR values than droplet size. NLR (R202)> NLR (D17). Therefore, NLR reflects two contributions: dispersion quality and droplet evolutions.