An object of the present invention is to produce and isolate a linear oligolactic acid thioester having a thioester group at the terminus as a single compound. According to the present invention, there is provided a compound represented by the formula (1) or a salt thereof: 1 wherein X represents a hydrogen atom or a protective group for a hydroxyl group; Y represents an aliphatic group, an aryl group or a heterocyclic group; and n represents an integer of 0 to 19.