Ternary polymer blends (TPB) based on polyurethane (PU) containing tertiary amine, poly(vinyl chloride) (PVC), and poly(styrene-co-maleic anhydride) (SMA) containing 6.25% maleic acid were prepared via solution technique. The blends were investigated by using differential scanning calorimetry (DSC), dynamic mechanical (DMA), stress-strain testing, and density. DSC, DMA and density results showed extensive molecular mixing of the three polymer components through ion pair-ion pair, ion pair-dipole and dipole-dipole interactions. The glass transition temperatures (Tg) of TPBs gradually merged from two distinct transitions to one transition temperature. The mechanical properties of TPBs exhibited synergistic behavior with respect to tensile strength and the stress-strain behavior similar to reinforced elastomers at low PVC or SMA contents and well-developed yield points, stress whitening and necking at high PVC or SMA contents.