The cholinergic system plays an important role in the immune response.Acetylcholinesterase (AChE) is a major component of the cholinergic system, which can control the level of acetylcholine (ACh).The AChE cDNA sequence was cloned from Chlamysfarreri by using rapid amplification of cDNA ends (RACE) approaches and expression sequence tag (EST) analysis.The full-length sequence analysis revealed an open reading frame (ORF) of 1569 bp encoding for a protein of 522 amino acids.The recombinant CfAChE had an apparent Mr of 70 kDa and 58 kDa before and after deglycosylation by SDS-PAGE.The predicted amino acid sequence of Chlamysfarreri AChE (desinated CfAChE) contained a signal peptide, the choline binding site, the aromatic residues of the catalytic gorge, the conserved active site and the substrate specificity site, and it showed 20.2%-29.0 % amino acid similarity with other AChE reported so far.