The structural behavior of a homologous series of thermotropic (4,4’-dihydroxybiphenylyl)-alkanedioic acid polyesters (PB-n, n indicates the number of methylene units in the spacer) with alkylene spacers ranging from n = 10 to n = 18 was studied using wide-angle X-ray diffraction under hydrostatic pressures up to 300 MPa. PB-10 shows an enantiotropic transition of crystal (K-1)-smectic H (S-H)-isotropic phase (I) in the whole pressure region. The long d spacing of the law-angle reflection for the Kr phase is constant in the crystalline state and then shrinks discontinuously by about 2.4 Angstrom at the K-1-S-H transition, while the d spacings of wide-angle reflections change gradually with temperature. Both d spacings of the K-1 crystal are slightly deformed by applying pressure. In PB-12 the same transition process is observed in the pressure region below 100 MPa, while the smectic B(S-B) phase is induced in place of the S-H phase under a higher pressure. On the other hand, PB-14-PB-18 polyesters exhibit a crystal polymorph (K-2) between the K-1 and S-H phases. In these polyesters, the long d spacing increases gradually by about 1-2 Angstrom with temperature during a broad K-1-K-2 transition. Then a longer d spacing of the K-2 phase shrinks rapidly at the K-2-S-H transition on heating. It is found that both K-1 and K-2 crystals are deformed substantially in the molecular chain direction by applying pressure, in contrast to a slight change in the d spacing of the SH phase. The structural behavior during the K-1-K-2-S-H-I transition process of PB-14-PB-18 polyesters is observed reversibly in the whale pressure region.