Weldlines on the surfaces of plastic parts are inevitable where molds have inserts, lattices, or multi-point gates. The presence of weldlines in areas of stress concentrations may lead to strength problems. Moreover, weldlines reduce the surface quality of the parts where there is no paint on. Therefore, countermeasures should be implemented in advance, especially for high quality parts with shining surface finish. This paper presents a method of reducing weldline problems by design of experiment - or DOE method. A systematic change in the various process parameters have been implemented in order to obtain a case where weldline is minimized. The weldline in parts produced under different conditions were quantified to show that there can be optimal injection condition which can offer minimal weldline width. The result showed that by changing the process parameters of the mold temperature, the melt temperature and the injection speed, an optimal point was reached for the test case where the weldlines became invisible to the naked eyes.