Fiber orientation and micromechanics should be understood for exact prediction of physical properties and deformation of anisotropic composite parts which are generally treated as homogeneous materials for flow simulation and transversely isotropic materials for structural analyses. Fiber orientation has a significant effect on the mechanical properties and final shape of injection-molded parts. Fiber orientations in glass fiber (GF) reinforced PBT composites were observed by using a microtomography (Micro-CT) and the three dimensional CT results agreed with the prediction. Mechanical properties of the anisotropic composites were estimated by coupled three dimensional flow and structural analyses in which the micromechanics and the fiber orientation were considered spontaneously. In order to verify the coupled FE simulation results a theoretical model and a simple Representative Volume Element (RVE) model were employed. The coupled 3D analyses were in good agreement with the experimental data and the simple RVE model predicted higher stiffness than the experiments but lower stiffness than theoretical upper bound.