Toll-like receptor (TLR) is one of the most important patternrecognition receptors in both invertebrate and vertebrateanimals. In previous study, three different kinds of TLRcDNAs (PtToll1-3) have been cloned from Portunus trit-uberculatus. In this study, a novel PtToll4 cDNA sequencewas identified in this crab. The PtToll4 ORF is predicted toencode 894 peptides with an initiating signal peptide, anextracellular LRRs domain, a transmembrane region, and anintracellular toll-interleukin-1 receptor domain. Based onthe sequence and phylogenetic analysis, PtToll4 distinctlyclustered with almost all crustacean tolls, which mostly clus-tered with some shrimp TLRs and Eriocheir sinensis Toll2 (EsToll 2). The real-time quantitative polymerase chainreaction analysis showed that the transcript of PtToll4 wasconstitutively expressed in tissues. In hemocytes, the tran-script of PtToll4 in large granulocytes is approximatelythreefold higher than in small granulocytes and hyalocytes.Moreover, the expression of PtToll4 could be moderatelyand shortly upregulated by Vibrio alginolyticus or lipopoly-saccharide challenge in the primary cultured hemocytes