Poly(butylene terephthalate) (PBT) was used as modifier for epoxy resin. With the incorporation of 7.5 wt% PBT, the resin became a gel as shown by rheological measurements in steady shear, thixotropic loop and dynamic shear mode. The gel was very stable on storage. An abrupt change of rheological properties occurred at the dissolution temperature of the PBT spherulites. The PBT modifier did not impair mechanical properties of the cured resins, yet a moderate improvement in toughness was achieved.