For preliminary research on the biology function of MKK4 in Fenneropenaeus chinensis in this study,full-length cDNA sequence of MKK4 gene in F.chinensis was cloned using RACE method and was named FcMKK4.The full-length of cDNA sequence of MKK4 is 2 064 bp,which contains a 214 bp 5'-UTR,629 bp 3'-UTR and 1 221 bp open reading frame(ORF)that encodes 406 amino acid residues.Its isoelectric point(PI)was 8.50 and molecular mass was 45.94 ku.Homology analysis revealed that the amino acid sequences of FcMKK4 were highly homogenous with MKK4 of other species,80% with Ixodes Scapularis,and 78% with Harpegnathos saltator.The phylogenetic analysis showed that F.chinensis FcMKK4 was in the same class with other arthropods' MKK4.The expression level of FcMKK4 gene in different tissues was analyzed by quantitative real-time PCR.The results indicated that the highest expression level of FcMKK4 gene was in muscle,and that in hepatopancreas was the second.Real-time PCR analysis showed that the expression level of FcMKK4 was up-regulated significantly in muscle,hepatopancreas,hemocytes,gill,heart,intestine and stomach after stimulation with ammonia-N stress,and FcMKK4 showed different expression profiles in different tissues.The results implied that FcMKK4 might play an important role in abiotic stress response in F.chinensis.