This thesis presents a study on the effect of magnetic field on the distribution and orientation of magnetic particles in injection moulding. The experimental work, using various materials such as polyester resin, nickel particles, polypropylene (PP), polycarbonate (PC) and methods (single component injection and co-injection moulding), has led to a deeper understanding of the mechanism that governs magnetic particle orientation under an external magnet in the complex environment of polymer injection. A simulation model was developed to provide a theoretical basis for realistic magnetic mould tool design. As there was no previous data available, it was hoped to elucidate some gUidelines by simulation experiments. In addition, the relationship between the rheological property of the polymer mixtures and the relevant moulding parameters such as tool temperature, melt temperature and speed of injection moulding was investigated using a comprehensive design of experiments methodology. It was found that the ferromagnetic nickel flakes remained magnetic enough to overcome the strong drag forces imposed on them by the polymeric fluid matrix and were able to be orientated. The focus of the experimental work was carried out using both the single component injection and co-injection moulding processes. A link was established between the melt temperature gradient and magnet effect. In the co-injection moulding experiments, it became clear, that the core melt had a longer residence time due to the thermal barrier provided by the skin melt and this facilitated a much more visible magnetic effect compared with samples produced using the injection moulding process.