At this time about 3% of products produced by "X" plastic factory does not reach the standard. This factory has a problem to minimize the amount of defects. Taguchi method is used to lower the level of product defects. From the field survey, all the suspected factors can be obatained and it is shown ini the fishbone diagram. From the suspected factors, the factory chose factors that are to be used ini the experiments. Experiments were conducted using those four factors : pellet material percentage (60%, 70%, 80%), temperature (217°C, 225°C, 233°C), injection pressure (92 Bar, 93 Bar, 94 Bar), screw speed (81%, 83%, 85%). Taguchi method provide the combination and number of experiments. From each level of defects condition, analysis was done to obtain the affecting variables. The results of analysis shows that the combination of pellet material (80%), temperature (225°C), injection pressure (93 Bar), screw speed (83%) can minimize the amount of defects to 0.3%.