The block copolyetheresters with hard segments of poly(alkylene-p, p'-bibenzoate) and soft segments of poly(tetramethylene ether) have been investigated by two x-ray diffraction techniques and differential scanning calorimetry (DSC). The results from the counter diffractometry technique indicate the effect of composition on the diffraction peaks and relative crystallinity of the block copolyetheresters. The results from the photographic technique not only show the presence of the diffraction peaks qualitatively, but also indicate the layer spacings relating to the smectic phase for certain block copolyetheresters. The successive DSC heating curve after cooling from the isotropic (I) state to a temperature below the I-S (smectic) transition but well above the S-K (crystalline) transition indicates the nature of the S-I transition for some block copolyetheresters. The S-I transition peak overlaps with the K-S transition peak, or is even replaced by a K-I transition peak. Thus it is difficult to distinguish between the K-S, S-I transitions and a K-I transition in second-run DSC heating curves for the block copolyetheresters.