Push-out method revealed that interfacial shear strength between PA 66 and glass fibers in long fiber-reinforced PA 66 , which was fabricated through direct-fiber-feeding injection molding, was 20% lower than that in conventional fiber-reinforced PA 66. Low interfacial shear strength was due to insufficient heat energy during the molding process. Vacuum heating process of long fiber-reinforced PA 66 increased the interfacial shear strength. Consequently, fiber reinforced-PA 66, which exhibits high strength and Young's modulus at both room and high temperature, was fabricated through increasing the fiber length and interfacial shear strength.