Blends from polyethylene (PE) and polystyrene-b-polybutadiene-b-polystyrene star block copolymers (SBS) (thermoplastic elastomers) are studied with polyolefine recycling in view. Each component, dispersed in a heterogeneous blend, exhibits a two-phase morphology. This structure is investigated by small angle X-ray scattering (SAXS) and compared to mechanical properties as a function of SBS grade and content. Increasing the SBS content one observes a vanishing PE-related long period reflection, while an SBS-related peak emerges. Best mechanical properties are obtained at concentrations, where the width of the observed long period reflection is broadest. For a quantitative analysis of the SAXS, the interface distribution function (IDF) analysis is employed. Data are fitted with a function modeling arrangement as well as disorder of domains inside the two different kinds of dispersed grains. The analysis yields that the observed broadening of the long spacing peak is caused only by an increased fluctuation of the thicknesses of amorphous layers in the PE stacks. This fluctuation again decreases for SBS concentrations beyond 15 wt %. The effect is strongest for blends containing the SBS grade with the lowest molecular weight and is discussed in terms of its compatibilization effect.