Injection-molded composite materials as fabricated from chopped glass fiber and poly(trimethylene terephthalate), PTT, are evaluated through physicomechanical and thermomechanical analysis. Differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) were used to measure the thermal properties of the above composites. The mechanical properties including impact properties, tensile properties, and flexure properties of these composites were tested with a United Testing System SFM-20. Results showed that impact strength, tensile strength and modulus, flexure strength, and modulus of glass fiber reinforced PTT composites were improved significantly with increasing fiber content. The simultaneous improvement of both stiffness and toughness of composite materials is one of the important findings of this investigation. It was found that the crystallization temperature of PTT increased and heat deflection temperature doubled through reinforcement with glass fiber. The tensile fractured surfaces are evaluated through environmental scanning electron microscopy (ESEM) for studying the interaction between fiber and the matrix.