Caspases are a conserved family of cysteine proteases characterized by specificity for aspartic acid and play an essential role in cell apoptosis. In the present study, a novel effector caspase (designated as EsCaspase-3/7-1) was identified from Chinese mitten crab Eriocheir sinensis. The open reading frame of EsCaspase-3/7-1 cDNA was of 972 bp, encoding a polypeptide of 323 amino acids. EsCaspase-3/7-1 contained an N-terminal prodomain and a conservative C-terminal CASc domain, with the conserved active site "QACRG". The mRNA transcripts of EsCaspase-3/7-1 were constitutively expressed in all the examined tissues with high expression level in hemocytes, hepatopancreas and gill. The EsCaspase-3/7-1 protein was mainly distributed in the cytoplasm of hemocytes. After Aeromonas hydrophila and lipopolysaccharide (LPS) stimulations, the mRNA expression level of EsCaspase-3/7-1 in hemocytes increased significantly. The mRNA expression level of EsCaspase-3/7-1 in hemocytes was significantly up-regulated after H2O2 treatment in vitro. The recombinant EsCaspase-3/7-1 protein (rEsCaspase-3/7-1) was capable of hydrolyzing the substrate Ac-DEVD-pNA rather than Ac-YVAD-pNA and Ac-VEID-pNA in vitro, and exhibited binding activity to LPS. These results demonstrated that EsCaspase-3/7-1 might act as an LPS receptor, and play an important role in the regulation of immune homeostasis of E. sinensis.