The warpage phenomena occurring frequently in the injection molded parts due to the inhomogeneous distribution of shrinkage are known as serious problems because those may shorten the life cycle of the product. Therefor, in this study the effect of the change of process condition, the change of the structure of injection molded parts and fiber orientation on shrinkage and warpage were investigated by performing an injection molding experiment using PBT(polybutylene terephthalate) resin including 30wt% glass fiber and a numerical simulation using Moldflow(series 9.02) software. From this study, it was found that the degree of warpage of the short sides was higher than that of the long sides in three dimensional molded parts, whereas the change of the process condition had more significant effect on the long sides rather than short sides with respect to degree of warpage. In addition, the experimental results showed that the degree of warpage increased with the increase of injection rate, but that of warpage decreased with the increase of packing pressure. And numerical simulation could adequately describe experimental results with a similar tendency. Especially, it was revealed that homogeneous temperature distribution over the corner of the three dimensional injection molded parts was the most crucial condition in order to minimize degree of warpage. It was effective to keep the cooling temperature of the inner side of the cavity lower than the outer one. Conclusively, fiber orientation and corner effect were found to be the principal causes of warpage from this study.