The melting behaviour of ethylene terephthalate (ET)-caprolactone (CL) random block copolyesters (TCLs) crystallized from the melt were studied by differential scanning calorimetry (d.s.c.). The TCLs with high ET contents showed three melting endotherms. Peaks I and II can be attributed to the melting of crystallites formed during primary and secondary crystallization processes respectively, and peak III is the fusion of crystals recrystallized during the d.s.c. heating scan process. For TCL having relatively lower ET content, another melting endotherm, corresponding to the fusion of crystallites of the CL segments, was observed, which indicated that the segregation occurred during the annealing process because of the nonuniformity of the chemical composition and sequence length distribution of the ET and CL segments in TCL copolyesters.