A suppressor of cytokine signaling 2 (SOCS-2) homolog was identified from the red crayfish Procambarus clarkii. Phylogenic analysis showed that P. clarkii SOCS-2 (Pc-SOCS-2) was very similar to that of invertebrates. The sequence contains a central SH2 domain, a conserved SOCS box, and a variable N-terminal domain. Real-time polymerase chain reaction showed that Pc-SOCS-2 mRNA level was higher in muscle and heart than in the other tissues examined. A 40-kDa recombinant protein was successfully expressed and purified from Escherichia coli cells as confirmed by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and Western blotting. Pc-SOCS-2 was significantly downregulated in the hepatopancreas after 20-hydroxyecdysone injection. Knockdown of Pc-SOCS-2 gene by small interfering RNA transfection in the hepatopancreas increased the expression levels of 20-hydroxyecdysone-responsive genes at 48 hr. Taken together, these results suggest that Pc-SOCS-2 is a negative regulator of ecdysteroid signaling transduction.