Smectic state morphology of the main-chain liquid crystal PB-14 polyester was studied by small-angle X-ray scattering (SAXS), differential scanning calorimetry, and transmission electron microscope methods. The PB-14 polyester forms isotropic liquid (I), smectic H (S-H), and crystalline phases in order of decreasing temperature. The transition temperature between the I and S-H phases was 226 degrees C on heating and 210 degrees C on cooling when it was measured at a rate of 10 degrees C min(-1). SAXS for the S-H phase formed from the isotropic melt showed well-defined reflection maxima which are attributed to the chain-folded lamellar structure. The lamellar size increased from 300 Angstrom to 500 Angstrom with an increase of the liquid crystallization temperature of 190 degrees C to 220 degrees C. The relationship between the lamellar thickness and isotropization temperature is well described by the Thomson-Gibbs equation. According to this relationship, the surface free energy of the lamellae and the equilibrium isotropization temperature of S-H were elucidated as 72 erg cm(-2) and 263 degrees C, respectively. When the sample was annealed at a SH temperature of 215 degrees C, the isotropization temperature of the S-H phase increased from 228 degrees C to 257 degrees C, and simultaneously the enthalpy change increased from 4.9 kcal mol(-1) to 6.0 kcal mol(-1). These trends can be explained by the lamellar thickening. The overall results thus indicate that the S-H liquid crystallization at a certain temperature takes place imperfectly in a finite period due to the chain folding and that the succeeding annealing causes the alteration of the chain conformation from a folded form to an extended one as observed in the crystallization of conventional polymers.