This paper discusses the microstructure related fracture behavior of short-fiber reinforced thermoplastics. The microstructure of injection molded weld was studied by microscopic methods and described fiber orientation. Injection welds are the place where two flow fronts come together and appears the fiber orientation such as flower and volcano-like pattern. The strength decrement of the parent and weld part are greatly affected by fiber orientation within the angle of 45°, but over 45° the effect of matrix on strength is greater than that of fiber orientation. The polymer composite materials used in the experiment are polycarbonate (PC) with amorphous structure as general engineering plastics included 30% short glass fiber and polyphenylene sulfide (PPS) with crystalline structure included 40% short glass fiber, the specimen used is the dumbbell type tensile specimen with a weld line by double gate injection mold. Microtoming technique was used for slicing ultrathin sections from molded polymer parts. Microstructural analysis of fiber orientation at injection weld was carried by the light transmission microscope (LM) and SEM.