The microstructure and mechanical properties of polyamide 12/isotactic polypropylene blends with different compositions are studied. It is shown that the injection moulding technique used to process all samples results in a more or less pronounced orientation of macromolecular chains, which in its turn is responsible for a preferential orientation of polymer crystals. At a larger scale, the injection technique is also responsible for the deformation of polyamide domains into ellipsoides when polypropylene is dominant. In contrast, when polyamide is dominant, domains of both polymers are co-continuous in the materials. This feature is discussed on the basis of dynamic mechanical measurements.