The phase behavior of a novel comb-shaped polyester (P8a12), synthesized from 2-[8-(4-(4-cyanophenylazo)-phenoxy)-octyl]-1,3-propanediol and tetradecanedioic acid, has becn studied by differential scanning calorimetry. It has been shown that the phase behavior of this polymer is strongly dependent of the thermal history. Up to four, partially overlapped endothermic effects have been found in the DSC heating scans, whose relative intensities markedly change with the conditions of the previous thermal treatment, as well as with the scanning rate. These effects have been tentatively associated with the transitions of as many different polymer structures. The thermal treatments needed for selectively developing the different structures inP8a12specimens have been determined. The structures have been preliminarily studied by X-ray diffraction and optical microscopy.