A series of ethylene terephthalate-epsilon-caprolactone copolyesters (TCL) with different hard segment contents were synthesized and characterized by GPC, NMR, and DSC. The analysis from high-field H-1-NMR reveals that the transesterification between ET and CL segments during synthesis is unavoidable, so TCL copolyesters are segmented copolyesters with certain random properties, as shown by the specific chemical and sequence structure of TCL copolyester chains and as confirmed by their crystallization behavior. The stress-strain test shows that TCL copolyesters with different hard segment contents may possess rubberlike or toughening plastic mechanical properties.