We have cloned the cDNA and genomic DNA of an active intronless cathepsin L from Metapenaeus ensis. The encoded enzyme has the shortest prosequence among cathepsin L subgroup. It was predominantly expressed in hepatopancreas with an expression level of at least 10 times higher than in any other tissues. It also has expression in stomach, intestine, eye, testis, ovary and muscle. Western blots visualized the mature enzyme in hepatopancreas and a procathepsin L in ovary, intestine and stomach. Metapenaeus cathepsin L (MeCatL) is localized in the large digestive vacuole of the digestive B cell of hepatopancreas. MeCatL has a role in food digestion. An interesting finding is that it exists in the nucleus of oocyte. MeCatL might have a specified physiological role in the nucleus of oocyte. MeCatL might also have a house-keeping function as is suggested for mammalian cathepsin L.