We identified the cDNA sequence of cathepsin L (CatL) in Macrobrachium nipponense, designated as MnCatL, for the first time. The MnCatL cDNA, isolated from the ovary, was 1710 bp in length, containing a 31-bp 5'-untranslated region, a 650-bp 3'-untranslated region, and an open reading frame of 1029 bp, encoding a 342-amino acid polypeptide with a predicted molecular mass of 37.7 kDa. The polypeptide is composed of an 18-amino acid signal peptide, a 106-amino acid propeptide and a 218-amino acid mature peptide. MnCatL mRNA was detected in all tissues that we examined, including the thoracic ganglia, heart, muscle, intestine, hemocytes, ovary, testis, gills, and hepatopancreas. MnCatL expression reached a maximum value in both hepatopancreas and ovaries at the later stages of vitellogenesis, suggesting that MnCatL is involved in ovarian maturation of the oriental river prawn. During embryogenesis, MnCatL expression decreased as the embryo developed. The expression of MnCatL in the ovary and embryo suggest that MnCatL plays an important role in the uptake of vitellogenin and yolk protein, which are deposited in the oocyte for ovary maturation and embryo development, during oogenesis and embryogenesis of M. nipponense.