Prostaglandin (PG) F2α is widely distributed in various organs and exhibits various biological functions, such as luteolysis, parturition, aqueous humor homeostasis, vasoconstriction, rennin secretion, pulmonary fibrosis and so on. The first enzyme reported to synthesize PGF2 was referred to as PGF synthase belonging to the aldo-keto reductase (AKR) 1C family, and later PGF2α synthases were isolated from protozoans and designated as members of the AKR5A family. In 2003, AKR1B5, which is highly expressed in bovine endometrium, was reported to have PGF2α synthase activity, and recently, the paper entitled ‘Prostaglandin F2α synthase activities of AKR 1B1, 1B3 and 1B7’ was reported by Kabututu et al. (J. Biochem.145, 161–168, 2009). Clones that had already been registered in a database as aldose reductases (AKR1B1, 1B3, and 1B7) were expressed in Escherichia coli, and these enzymes were found to have PGF2α synthase activity. Moreover, in the above-cited article, the effects of inhibitors specific for aldose reductase on the PGF2α synthase activity of AKR1B were discussed. Here, I present an overview of various PGF/PGF2α synthases including those of AKR1B subfamily that have been reported until now.