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Copolyesters of poly(tetramethylene terephthalate) (PTMT) and p-hydroxybenzoic acid (PHB) are obtained by means of transesterification in the molten state using different ratios of the starting reagents. After treatment with trifluoroacetic acid, the total reaction product could be divided into a soluble part and an insoluble one, differing in the tetramethylene terephthalate/oxybenzoate (TMT/OB) units ratio. It was proved by 1H NMR that the fraction of OB units in the soluble part of the copolyester varies from 3 to 12 mol-% for PHB feed contents of 10–80 mol-%. There is no systematic influence of the PHB feed content on the copolyester composition. The maximum OB content was achieved at 20 mol-% PHB in the starting mixture. The results from 13C NMR, DSC, WAXS and crystallization kinetics measurements suggest the presence of blocks of TMT units in the macrochains. The observed thermal properties and crystalline structure are explained in terms of the inhomogeneity of both chemical composition and units sequence in the total reaction products. This leads to the coexistence of at least two phases differing mainly in their content of OB units.