In this work the effect of the presence of a thermotropic liquid crystalline polymer (TLCP) on the physical ageing of poly(ethylene terephthalate) (PET) was investigated. Physical ageing of PET and its blends with a TLCP was carried out by annealing the samples at 60 degreesC for several ageing times. Structural relaxation has been revealed by DSC through the analysis of position and magnitude of the endothermic peak superposed on the glass transition. It was found that the peak increases and shifts towards higher temperatures as the annealing time increases for all materials analysed. With respect to the PET matrix, blends submitted to physical ageing show an increase in the ageing rate by a percentage that increase with the amount of TLCP. Moreover, increasing the fraction of liquid crystalline component, a continuos decrease of the cold crystallisation temperature has been also observed.