Thermoplastic elastomers based on poly (butylene terephthalate) (PBT) and poly (ethylene glycol) (PEG) were studied by bending-creep measurements. The dependence of the creep compliance on the composition of the block copolymer was determined, and the experimental results were compared with calculated results to obtain a better understanding of structure-property relationships for this class of materials. The hard PBT domains in the rubbery PEG matrix make a large contribution to the mechanical strength and hardness, presumably serving as reinforcing fillers as well as cross-links. Relaxation effects were found to decrease significantly with increase in hard-segment content.