Molting in shrimp is controlled by the molt-inhibiting hormone (MIH) and ecdysone. MIH inhibits the synthesis of ecdysone in the Y-organ, resulting in molt suppression; it is a neuropeptide member belonging to the eyestalk CHH/MIH/GIH family. The cloning of MIH (formerly MIH-like) of the shrimp Metapenaeus ensis has been reported in a previous study. To obtain a large quantity of fusion protein for antibody production and biological assay, the cDNA encoding the shrimp MIH was inserted into the pRSET bacterial expression vector. His-tagged fusion protein was produced and purified by an Ni2+-charged affinity column. Polyclonal antibody to rMIH was subsequently obtained by immunizing rabbits with purified recombinant proteins. Results from Western blot analysis indicated that the antibody was specific. Furthermore, results from immunocytochemical analysis showed that specific cells in three different clusters of the X-organ, the sinus gland and the axonal tract of the eyestalk contain MIH. To test for the molt-inhibiting activity of rMIH, shrimp at intermolt stage were injected with rMIH and the molt cycle duration of the injected shrimp was monitored. A significant increase in molt cycle duration was recorded for the shrimp injected with the recombinant protein.