In this work, the effects of adding small amounts of amorphous nylon (a-nylon) on the properties of poly(butylene terephthalate)(PBT) have been studied. Miscibility and properties of PBT/a-nylon blends were compared with those of PBT/nylon 6 blends. Blends were prepared in a twin-screw extruder. The compositions of a-nylon or nylon 6 were varied from 0 to 20 phr. Rheological, thermal, mechanical, and dynamic mechanical properties of the blends were examined using a capillary rheometer, a differential scanning calorimeter (DSC), a universal testing machine (UTM), and a Rheometrics Mechanical Spectrometer(RMS), respectively. The PBT showed a single endotherm around 225.4 degrees C on the DSC thermogram at the first heating scan but exhibited a second endotherm at a temperature below that of the original endotherm at the second heating scan. When a-nylon was added, the original endotherm was remarkably affected, but the second endotherm was not appreciably changed; i.e., the heat of fusion at the original endotherm decreased linearly with increasing a-nylon content, meaning that the addition of a-nylon affects significantly only the higher-melting crystals of PBT. The impact strength of PBT was decreased with nylon 6 content but was increased with increasing content of a-nylon. With an increase in the a-nylon content, the tensile modulus and the flexural modulus of PBT were decreased. Of interest is, however, that the tensile strength was significantly increased with a-nylon up to 15 phr. The melt viscosity of PBT was decreased with increasing a-nylon content, whereas it was not significantly changed with nylon 6 addition; i.e. the addition of a-nylon acted as a lubricant or a processing aid for PBT. The dynamic mechanical and the morphological studies showed that PBT was more miscible with a-nylon than with nylon 6. It was also found that a-nylon exhibited a compatibilizing effect for the PBT/nylon 6 blend of 70/30 wt% composition.