This study summarizes the importance of melatonin in different plants and fungi. In this review, we discussed the biosynthetic pathway of melatonin, its metabolites, and its oxidative reduction. Melatonin is a molecule derived from tryptophan, with pleiotropic activity. It is present in nearly every organism. Its synthetic course depends on the organism in which it resides. The tryptophan to the melatonin pathway, for example, varies in plants and animals. It is thought that the synthetic mechanism for melatonin was inherited in eukaryotes from bacteria caused by endosymbiosis. Nevertheless, the synthetic pathways of melatonin in microorganisms are unknown. The metabolism of melatonin is exceptionally complex with these enzymatic processes developed out of cytochrome C. As well as the enzymatic degradation, melatonin is metabolized by interactive pseudoenzymes and free radicals processes.