The transformer-2 gene (tra-2) plays a key role in the sexual differentiation regulatory hierarchy. In this study, tra-2 gene homologs designated as Mntra-2 was cloned and characterized from Macrobrachium nipponense. The full-length cDNA of Mntra-2 consists of 1724 bp with an open reading frame (ORF) encoding 192 amino acids, an 827 bp 5′-untranslated region (UTR) and a 318 bp 3′-UTR. The predicated molecular mass of Mntra-2 was 20.805 kDa with an estimated theoretical isoelectric point of 10.36. The deduced amino acid sequence shares high homology with Penaeus monodon. Real-time quantitative polymerase chain reaction (RT-qPCR) analyses demonstrated that the expression levels of Mntra-2 varied significantly during different developmental stages of embryogenesis, larvae, and post-larvae and in various adult tissues. During embryogenesis, the expression level of Mntra-2 was slightly higher at the cleavage stage than at the blastula stage, and reached the highest level at the nauplius stage. During the larvae, the Mntra-2 expression gradually increased from 1 d larvae post hatch (L1) to L10 and decreased to a lowest level at the end of metamorphosis. During the post-larvae, the Mntra-2 expression was higher level at the 5 d after the metamorphosis (P5). RT-qPCR showed the Mntra-2 mRNA was expressed in ovary, testis, muscle, heart, abdominal ganglion, brain, and intestine with the highest level of expression in muscle and intestine. The results indicate that Mntra-2 is an arthropods tra-2 homolog and probably plays important roles in embryonic development and sex differentiation of M. nipponense.