Metallothionein is a cysteine-rich protein with a high content of metal ions, widely found in nature. It is known for its potent antioxidant properties and heavy metal detoxification capabilities. The high sulfhydryl content of metallothionein allows it to effectively scavenge free radicals and reduce oxidative stress, making it useful in neuroprotection, anticancer, and anti-inflammatory activities. Metallothionein can also play a role in environmental heavy metal pollution control, disease prediction and diagnosis, and the development of skincare and health foods. This review summarizes recent advances in the classification, structure, biological functions, and applications of metallothionein, focusing on its antioxidant effects and related functions. Metallothionein's diverse biological functions and broad application prospects in various fields are highlighted, along with the need for further research to understand its complex mechanisms and structures in different species.Metallothionein is a cysteine-rich protein with a high content of metal ions, widely found in nature. It is known for its potent antioxidant properties and heavy metal detoxification capabilities. The high sulfhydryl content of metallothionein allows it to effectively scavenge free radicals and reduce oxidative stress, making it useful in neuroprotection, anticancer, and anti-inflammatory activities. Metallothionein can also play a role in environmental heavy metal pollution control, disease prediction and diagnosis, and the development of skincare and health foods. This review summarizes recent advances in the classification, structure, biological functions, and applications of metallothionein, focusing on its antioxidant effects and related functions. Metallothionein's diverse biological functions and broad application prospects in various fields are highlighted, along with the need for further research to understand its complex mechanisms and structures in different species.