The giant freshwater prawn， Macrobrachium rosenbergii， is an important aquaculture species. A better understanding of the molecular components of reproduction in this species would help to advance the prawn production. In the present study， we demonstrated the presence of an egg laying hormone (ELH)-like peptide in the male reproductive system. First， an antibody to the abalone (a)ELH was generated， and by Western blot it was shown to specifically bound to a protein from the male M. rosenbergii reproductive tissues with a similar size to molluscan ELH. This aELH-like peptide was localized in spermatogonia in the testes of all three male morphotypes: blue claw， orange claw and small males. Moreover， the aELH-like peptide was detected in the epithelium of the spermatic duct and its associated smooth muscle cell layers and on the outer surface of spermatozoa. As well， the aELH-like peptide was detected in the spermatophore located in the female thelycum at 4-6 h post-mating， indicating that it was transferred to the female during copulation. Taken together， we suggest that this aELH-like peptide could be as a male inducing factor that helped to accelerate female spawning. Liquid chromatography of crude extracts and immunoblot analysis suggested that the aELH-like peptide could be further purified for ultimate characterization.