The effects of fiber content and fiber orientation on the mechanical properties and the fatigue strength of a short-fiber reinforced plastic were investigated. Thin plates of carbon short-fiber reinforced polycarbonate were injection molded. An image processing analyzer was used to measure the fiber content and the fiber orientation. The distribution of fiber length was almost unique irrespective of the fiber content. The hardness, Young's modulus and tensile strength became higher with increasing the fiber content. Smooth specimen and center-notched plate were fatigued under cyclic tension-compression. The propagation behavior of fatigue cracks was observed together with the measurement of crack closure. The fatigue strength at finite life and the resistance of crack propagation became higher with increasing the fiber content. The relation between crack propagation rate and the effective stress intensity factor divided by the Young's modulus was almost unique, irrespective of the fiber content or fiber orientation.