Pressure effect on the melting behavior of poly(butylene terephthalate) (PBT) and poly(hexamethylene terephthalate) (PHT) was studied by high-pressure DTA (HP-DTA) up to 320 and 530 MPa, respectively. Cooling rate dependence on the DSC melting curves of the samples cooled from the melt was shown at atmospheric pressure. Stable and metastable samples were prepared by cooling from the melt at low and normal cooling rates, respectively. DTA melting curves for the stable samples showed a single peak, and the peak profile did not change up to high pressure. Phase diagrams for PBT and PHT were newly determined. Fitting curves of melting temperature (T m ) versus pressure expressed by quadratic equation were obtained. Pressure coefficients of T m at atmospheric pressure, dT m /dp, of PBT and PHT were 37 and 33 K/100 MPa, respectively. HP-DTA curves of the metastable PBT showed double melting peaks up to about 70 MPa. In contrast, PHT showed them over the whole pressure region. HP-DTA of stable poly(ethylene terephthalate) (PET) was also carried out up to 200 MPa, and the phase diagram for PET was determined. dT m /dp for PET was 49 K/100 MPa. dT m /dp increased linearly with reciprocal number of ethylene unit. The decrease of dT m /dp for poly(alkylene terephthalate) with increasing a segmental fraction of an alkyl group in a whole molecule is explained by the increase of entropy of fusion.