Diseases caused by viruses, especially white spot syndrome virus (WSSV), are the greatest challenge to worldwide shrimp aquaculture. Therefore, the innate immunity of shrimp has attracted extensive attentions these years. To date, however, no mechanism of immuno-related signal transduction pathway has been reported. In this investigation, an important signal transduction factor-Ran gene encoding ras-related nuclear protein (Ran protein) was characterized in shrimp. The shrimp Ran gene, without introns when compared with genomic DNA, was 645 bp in length. The GTP-binding assay showed that the Ran protein had GTP-binding activity. The results of RT-PCR and Western blot indicated that the transcript and protein of Ran were detected in every tissue of shrimp including hepatopancreas, haemolymph, gill, intestine, heart and muscle. In the WSSV-resistant and WSSV-infected shrimp at 4h postinfection, the Ran gene was obviously up-regulated, indicating that it played a role in shrimp immunity against virus infection. This study, therefore, might provide a clue to elucidate shrimp innate immunity.