In injection‐molded parts made of fiber reinforced thermoplastics, large warpages are frequently observed. The warpage is caused by anisotropic mechanical properties yielded by fiber orientations in molded parts. Therefore, it is necessary to predict fiber orientations and anisotropic mechanical properties for estimating the occurrence of warpages. A computer program for evaluating fiber orientation in molded parts was developed by using Folgar and Tucker’s planar orientation model that was considered as fiber–fiber interactions. The classical laminated plate theory was applied to predict mechanical properties (elastic modulus and thermal expansion coefficient) of molded parts in this study. The mechanical properties were predicted in the analysis from calculated fiber orientations and mechanical properties of the fiber and the polymer. Predicted elastic modulus and thermal expansion coefficient were compared with measured ones for a molded plate of glass‐fiber‐reinforced nylon‐6,6 (fiber content 30 wt. %) to verify computational method. Predicted results agreed with measured ones very well for both the elastic modulus and the thermal expansion coefficient.