Abstract: Poly (glycolic acid) (PGA) is an environmentally friendly, biodegradable polymer commonly utilized in biomedical applications. Due to its high thermal deformation temperature, favorable mechanical properties, and effective gas barrier capabilities, PGA has potential application as food contact materials. However, current regulations do not explicitly involve the use of PGA in food contact applications, particularly the migration of oligomers. The potential migration of oligomers from PGA into food must be carefully considered. In this study, a method of ultra-high-performance liquid chromatography coupled with quadrupole time-of-flight mass spectrometry (UHPLC-QTOF MS) was developed for the determination of PGA oligomers. The migration of oligomers in three distinct scenarios were investigated, i.e. packaging for frozen food, disposable containers with heat packaging for short-term storage, and containers for hot food and beverages. These scenarios were assessed in various food simulants, including acidic foods, non-acidic foods, and alcoholic beverages. The results showed that a total of 21 oligomers in PGA samples are identified, including 12 linear oligomers and 9 cyclic oligomers. Notably, the retention time of these oligomers increases with the increase of number of polymerization units. When PGA was employed as packaging for frozen foods, no oligomers are detected in food simulants containing 4% acetic acid, 10% ethanol, or 50% ethanol. In contrast, a variety of linear and cyclic PGA oligomers are identified in the three food simulants when PGA was used for disposable containers with heat packaging and for hot food and beverages. This is particularly evident for linear oligomers GA5 to GA8 and cyclic oligomers GA6 to GA8. The potential mechanisms underlying the migration and formation of these oligomers can be explained that the non-crystalline regions of PGA are an amorphous state, where ester bonds are prone to gradual hydrolysis, facilitated by the diffusion of water molecules. This hydrolysis leads to the cleavage of chain segments, resulting in the generation of long-chain oligomers. Short-chain oligomers, characterized by lower molecular weights, exhibit a higher tendency to migrate into surrounding solutions, particularly within the non-crystalline regions formed by the degradation of long-chain oligomers. Furthermore, short-chain oligomers can undergo self-reorganization from a disordered to an ordered state, facilitating the formation of both linear and cyclic oligomers. Temperature also significantly influences the formation of PGA oligomers, and elevated temperatures lead to a greater variety of oligomers and increased migration concentrations. Therefore, the migration of PGA oligomers into food should be carefully considered in scenarios involving the storage of acidic foods, non-acidic foods, and alcoholic beverages at high temperature.