The deformation properties under a tensile load of poly(c-caprolactone) (PCL) were compared to those of PCL/PVME and PCL/SAN mixtures. The critical strains at the end of the Hooke range (point A) and at the yield point (point B) remain unchanged. The critical strain marking the beginning of a disintegration of the blocklike crystallites and a fibril formation (point C) is generally affected for the PCL/PVME mixture only slightly but for the PCL/SAN mixtures quite strongly. As it appears, the swelling of the amorphous regions by PVME does not much change the entanglement density, whereas an inclusion of SAN does this and thus reduces the shear modulus. For a smaller modulus the strain required to produce the stress leading to a disintegration of the blocks becomes larger. Prior to the mechanical tests, a structural characterization of the different blends was carried out by SAXS and DSC. As was found, the presence of a second noncrystallizable compound does not change the crystal thickness and results only in an expansion of the amorphous intercrystalline regions.