A highly efficient strategy for synthesizing the first biocompatible polyesters with ALE characteristics has been established via immortal ring-opening polymerizations of cyclic esters bearing nonluminophores. In the process, the large excess hydroxyl-modified ATE active compound, acting as the chain transfer agent, attaches to the active rare-earth metal catalyst via the rapid-reversible exchange reaction to initiate the polymerization. Thus, more polyester chains appear to grow from one active metal species, and the AIE fragments are incorporated into the polymer chains at specific sites, in situ. The resultant polyesters have linear, block, or star-shaped microstructures mimicking those of the modified ATE compounds. The polymerization solutions can be directly fabricated to large-area thin solid films. The obtained PLA, for instance, emits fluorescence in water/THF mixtures owing to aggregation, the intensity of which is 2850-fold stronger than that in THF solution. This strategy avoids complicated preparation of ATE-active monomers and/or usage of toxic metal reagents for catalyzing the coupling reactions in order to introduce ALE-active fragments, which provides a straightforward approach to access ATE active or other functional polymers from hardly modified monomers.