The gas-assisted injection moulding process is a technique in the polymer processing industry developed to overcome the limitations of the conventional moulding process in manufacturing of parts with thick and non-uniform sections. However, due to the two-phase flow situation, optimisation of the process is difficult to perform since there are a number of quality indices, such as gas bubble volume, gas fingering, and gas blow through, to consider and optimise. In the present paper process optimisation work has been carried out using the Taguchi design of experiment method to optimise the processing conditions that gives optimised gas content within the moulded part and yet lower the possibility of part defects such as gas blow through and gas fingering.