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Recycling of waste poly(ethylene terephthalate) (PET) has attracted much attention in recent years because of the pressure from the environment. However, the cost-effective conversion of waste PET into value-added products by ecofriendly methods remains to be a challenge in the industry. In this work, a method for converting PET into calcium terephthalate by reactive melt processing was developed and investigated. Specifically, PET pellets were blended with calcium hydroxide powders using reactive melt processing, and the resulting mixture was converted into calcium terephthalate by simple hydrolysis in water. Physicochemical characterizations for morphologies, chemical compositions, and thermal properties were conducted to investigate intermediate components produced during the process, as well as the mechanisms of this new process. The results indicate that the effective transformation of molten PET into calcium terephthalate may be attributed to several factors, including the strong mechanical interaction during melt mixing, the thermal decomposition of PET chains to form carboxylic end groups, and the catalytic nature of calcium hydroxide in PET hydrolysis. This research can lead to a cost-effective route for the upcycling of waste PET into a value-added product that may be useful in demanding and emerging applications. [ABSTRACT FROM AUTHOR]