Abstract: An L9 experimental matrix design based on Taguchi method was conducted to optimize the tensile strength of injection-molded glass fiber-reinforced PA66 (Zytel 70G33L) with and without weld lines. Based on a standard analysis of variance (ANOVA), it has been found that the relative significance of each factor on the weld line strength is arranged in decreasing order of melt temperature (F=70.98%), packing pressure (F=14.12%), injection velocity (F=13.14%) and injection pressure (F=0.82%). Under the optimum factors levels, the predicted optimum tensile strength is 156.44MPa and in good agreement with the confirmative experimental result 164.987MPa, while the weld lines are strengthened approximately by 20%~50%.