The microstructure of semi-crystalline thermoplastics has an important influence on the physical properties of extruded and moulded compounds. Plastics processing methods develop different morphologies in polymers depending on the process and processing conditions applied. This paper features the control of morphology in isotactic polypropylene and polyethylene processed by injection moulding. Both conventional injection moulding and shear controlled orientation injection moulding (SCORIM) were used in the production of bars for the purpose of characterization of microstructure and physical properties. SCORIM provides for substantial control over the morphology of moulded thermoplastics. A high degree of molecular alignment can be achieved via SCORIM processing which contributes to enhanced stiffness and impact strength. It is possible to enhance stiffness without sacrificing impact resistance. The enhancement in stiffness is mainly attributed to the ’shish-kebab’ morphology developed in SCORIM, and both polypropylene and polyethylene exhibit shish-kebab microstructures. The principles of the development of molecular alignment using SCORIM as explained in this paper can be extended to other thermoplastics.