The cytMnSOD and mtMnSOD genes were cloned from hepatopancreas of Macrobrachium nipponense using the rapid amplification of cDNA ends(RACE)method for the first time.The full-length cDNA of cytMnSOD was 1 233 bp with a 858 bp of open reading frame(ORF)encoding a 286 amino acids(aa)protein with a 60 aa leader sequence; whereas the full-length cDNA of mtMnSOD was 1 113 bp with a 654 bp of ORF encoding a 218 aa protein with a 21 aa signal peptide sequence in the N-terminus.The calculated molecular masses and estimated pI of translated cytMnSOD and mtMnSOD proteins were 31.33 ku,24.05 ku and 5.62,7.12,respectively.The deduced amino acid sequence of cytMnSOD had 40% of similarity to that of mtMnSOD. Both cytMnSOD and mtMnSOD contained a manganese superoxide dismutase domain(DVWEHAYY),four conserved amino acids responsible for binding manganese(H110,H158,D243,H247 and H48,H96,D180,H184),and two N-glycosylation sites(NHT,NMS and NHT,NLS).The constructed phylogenetic tree indicated that arthropod MnSODs could be classified into two distinct branches,cytMnSODs,and mtMnSODs.The MnSODs from M.nipponense were more closely related to Macrobrachium rosenbergii MnSODs than that from other crustaceans.Real-time RT-PCR analysis showed that both cytMnSOD and mtMnSOD from M.nipponense were expressed in hepatopancreas,muscle,haemocytes,ovarian,mandibular organ and gill,but relatively higher in the hepatopancreas.The levels of both cytMnSOD and mtMnSOD transcripts in hepatopancreas were the highest in stage C among the molt cycle.Injection of pathogenic bacteria Aeromonas hydrophila resulted in the significant increase of cytMnSOD and mtMnSOD expressions 3 h after treatment,indicating that MnSOD may act as an important molecule involved in immune defense against A.hydrophila.