The compatibility, morphology, and mechanical properties of poly-ϵ-caprolactone (PCL) blended with poly(vinyl chloride), nitrocellulose, and cellulose acetate butyrate are described in this study. Methods used in this investigation included differential scanning calorimetry, dynamic mechanical testing, small-angle light scattering, light microscopy and stress–strain testing. Blends of PCL with poly(vinyl chloride) (PVC) are shown to be compatible in all proportions. In the PCL concentration range 40–100%, the PCL crystallizes in the form of negative spherulites. The spherulites were found to be volume filling with as much as 35% PVC. The nitrocellulose blends with PCL exhibited the glass transition behavior of a compatible system over the composition range of 50–100% PCL. At lower PCL concentrations, phase separation was apparent. The PCL crystallinity was present only in the nitrocellulose blends with more than 50% PCL, and it was in the form of rod-like super-structures. Blends of PCL with cellulose acetate butyrate were shown to be phase separated, with one phase having nearly equal proportions of the two polymers. The PCL crystallinity was in the form of negative spherulites and was formed with PCL compositions as low as 50%. Stress–strain results show polycaprolactone to be an effective plasticizer for poly(vinyl chloride) and the cellulose derivatives studied.