The influence of rubber particle spatial distribution on the toughening and stiffening efficiency of poly(vinyl chloride) (PVC)/nitrile rubber (NBR) blends is quantitatively studied. Blends with the pseudonetwork morphology or the morphology of well-dispersed rubber particles are used to elucidate the influence. The spatial distribution and matrix ligament thickness considerably affect the impact strengths of PVC/NBR blends. On the other hand, the tensile modulus of the blends is a function of rubber content but not of particle spatial distribution. Quantitative analysis shows that the modulus for the blend with the pseudonetwork morphology is much higher than that for the blend with the morphology of well-dispersed rubber particles for the same values of rubber particle size, size distribution and high impact strength. The dependence of toughening and stiffening efficiency on the spatial distribution is stronger than on the matrix ligament thickness. The pseudonetwork morphology is thus demonstrated to be very efficient in generating PVC/NBR blends simultaneously with high toughness and high stiffness.