Polymer blends consisting of miscible components may form single phase structures; however, it requires solution blending to ensure complete homogeneity. For a large scale mixing, however, mechanical blending is the common practice. The resulting blends are homogeneous on the macroscale, but often contain microscopic domains of the component polymers as well as domains of mixed phases. This work describes mechanical blends of PVC with miscible polymers (nitrile rubber, poly-e-caprolactone, and a copolyester thermoplastic elastomer). The complex morphology of these blends has been studied and identified by means of the frequency- and temperature-dependence of their viscoelastic behavior.