Although tropomyosin (TM) is known as a major allergen of crustaceans, few study has been carried out on it in China. In this study, three tropomyosin genes were amplified by polymerase chain reaction (PCR) from three species of crab (mud crab, Scylla serrata; Chinese mitten crab, Eriocheir sinensis; Japanese blue crab, Portunus trituberculatus), respectively. Sequence analysis showed that all the three cloned DNA fragments had the open reading frame (ORF) of 855 bp, encoding proteins with 284 amino acid residues and molecular weight of approximately 34 ku. The three TMs revealed extremely high identity to TMs from other crustaceans. The tropomyosin of mud crab was further studied by recombining with the vector pGEX-4T-3, and over expressed in E. coli JM109. A major protein band with size of about 61 ku was observed on SDSPAGE, which is close to the predicted molecular weight of the target fusion protein GST-TM. The expressed protein was water soluble and was further purified by GST affinity column. Westernblot analysis using both antimud crab TM polyclonal antibody and sera from subjects with crustacean allergy revealed positive reaction to the GST-TM fusion protein, strongly suggesting that the expressed protein is allergenic and can be used as a potential antigen for allergy diagnosis.