In biochemistry, thioesterases are enzymes which belong to the esterase family. Esterases, in turn, are one type of the several hydrolases known.
Thioesterases exhibit esterase activity (splitting of an ester into an acid and an alcohol, in the presence of water) specifically at a thiol group (−SH).
Thioesterases or thiolester hydrolases are identified as members of EC 3.1.2.