Abstract: Relish and Dorsal, members of nuclear factor-κB (NF-κB) family protein, play crucial role in immune response in Arthropoda. In this study, the cDNA sequences of Relish and Dorsal were cloned by rapid amplification of cDNA ends (RACE). There are 3254 nucleotides in Pt-Rel with a putative open reading frame (ORF) of 2949 bp that encodes a polypeptide of 983 amino acid residues. The Pt-Dor cDNA was 2348 bp in length including an ORF encoding a polypeptide of 637 amino acid residues．Prediction of protein domains revealed that both Pt-Rel and Pt-Dor contained typical NF-κB family structures RHD (Rel homology domain) and IPT (Immunoglobulin-like fold, Plexins, Transcription factors). Alignment of amino acid sequences for Pt-Rel and Pt-Dor revealed high identities with other arthropodas orthologs. Phylogenetic tree analysis based on amino acid sequences showed that the Pt-Rel and Pt-Dor were distinctly clustered with crustaceans Relish and Dorsal, respectively, but separated from insect orthologs. Pt-Rel and Pt-Dor were expressed in all tested tissues with the highest level in hemocytes. Three different pathogenic microorganism significantly induced both Pt-Rel and Pt-Dor expression in primary cultured crab hemocytes at 2h by Candida lusitaniae infection and 4h by Staphylococcus aureus and Vibrio alginolyticus challenge. These data suggest that Pt-Rel and Pt-Dor might be involved in host defense against to microbial pathogens in Portunus trituberculatus.