In this study, we obtained the full length of the SpCactus gene by RACE technology from Scylla paramamosain(SpCactus). And we analyzed the biological information of the SpCactus and its immune response under pathogen stimulation. The full length of SpCactus mRNA contains a 5' untranslated region (UTR) of 228 bp, an open reading frame of 1 311 bp and a 3' UTR of 496 bp. The SpCactus protein contains five characteristic ANK homology domains and showed 62% identity (73% similarity), 24% identity (36% similarity), and 9% identity (18% similarity) to the Litopenaeus vannamei Cactus (LvCactus) protein, the Drosophila melanogaster Cactus (DmCactus), and the Homo sapiens IκB protein, respectively. Prediction of the protein physicochemical properties of SpCactus revealed that it is a hydrophilic protein. By physical and chemical properties analysis, SpCactus was a hydrophilic protein. And its isoelectric point (pI) is 4.91. The mRNA of SpCactus showed high expression in the muscle, eyestalk and heart, but low expression in the hepatopancreas. Moreover, the expression of SpCactus were significantly upregulated by stimulation with Staphylococcus aureus and lipopolysaccharide. In this study, SpCactus gene was successfully cloned and characterized for the first time, and its bioinformatics analysis, physical and chemical properties were predicted. The biological functions of SpCactus gene were preliminarily explored, providing a basis for further study of its biological functions in immune response.