The effect of the poly(acrylic acid) homopolymer [PAA] existing in poly(propylene-graft-acrylic acid) [PP-g-AA] on the morphology and rheological properties of a PP-g-AA and polystyrene [PS] blend with varying amounts of poly(styrene-ran-glycidyl methacrylate) [PS-GMA] was investigated. Two different PP-g-AAs, one with PAA, [PP-g-AA(O)] and the other without PAA, [PP-g-AA(T)], were used. We have shown that when the amount of PS-GMA is increased, the dispersed domain size of PP-g-AA(O) in the PP-g-AA(O)/PS blend does not decrease, even when the amount of PS-GMA in the blend is as large as 25 wt%. Conversely, the dispersed domain size of PP-g-AA(T) in the PP-g-AA(T)/PS blend does decrease gradually and reaches a steady value. However, the reduction in the dispersed domain size (D-r) for PP-g-AA(T) in the PP-g-AA (T)/PS blend with PS-GMA was just 30%. Here, D-r is defined by the dispersed domain size of the blend without PSGMA minus that with 15 wt% of PS-GMA divided by the former. The changes in rheological properties with the proportion of PS-GMA content in the PP-g-AA(T)/PS blend were different to those for the PP-g-AA(O)/PS blend, thus demonstrating that the presence of PAA significantly affects the rheological as well as the morphological blend properties.