Glutathione S-transferases (GSTs: EC 2.5.1.18) represent a major group of detoxification enzymes. All eukaryotic species possess multiple cytosolic and membrane-bound GST isoenzymes, each of which displays distinct catalytic as well as noncatalytic binding properties. Plant GSTs detoxify a diverse range of xenobiotics and endobiotic substrates by catalyzing their conjugation with reduced glutathione (GSH, γ-glutamyl-cysteinyl glycine). Some GSTs also function as GSH-dependent peroxidases or reductases to detoxify toxic carbonyl-, peroxide-, and epoxide-containing metabolites produced within the cell by oxidative stress. More recent hypotheses suggest that the main role of plant GSTs is to act as binding proteins (ligandins). They are involved in intracellular transport of numerous non-substrate ligands. Several of the compounds including endogenous substrates and non-substrate ligands often decrease GST activity towards xenobiotics. Although various GST inhibitors have been identified and utilized in animal research, there have been relatively few studies on plant GST inhibitors. However, study of the inhibition of GSTs might be valuable for searching for physiological substrates and non-substrate ligands of the enzymes. In this review, availabe information on plant GST inhibitors is summarized.