In this Paper, the application of Taguchi Method (TM) on the process parameters of Injection Moulding of Polybutylene Terephthalate (PBT) is presented. The influence of process parameters, such as Injection Pressure, Suckback Pressure, Injection Time, Cooling Time, Zone 1 Temperature & Zone 2 Temperature (Barrel Temperatures) on Dark Spots and Short Shots (defects) were investigated using the Orthogonal Array L16 of Taguchi Method for 6 factors at 2 levels each with the response being percent defectives. It was found that Injection Pressure, Injection Time & Zone 1 Temperature had a major effect on the response. After the application of Taguchi Method, the rejection rate dropped down to 5.84% from 11.33%, which is a 48.45% reduction.