The pearl oyster,Pinctada fucata,is the most important species cultured widely for production of marine pearls in the coastal provinces of South China,while mass mortalities of the cultured pearl oyster have occurred frequently in juvenile,mother and operated oysters.Understanding the immune defense mechanisms of the pearl oyster may contribute to the development of novel management strategies for diseases control and the long-term sustainability of pearl industry.In this study,a suppression subtractive hybridization(SSH)cDNA library was constructed from the hemocytes of P.fucata challenged with Vibrio alginolyticus,and β-actin gene was used as internal control to estimate the efficiency of subtractive cDNA.A total of 600 clones in the SSH library were randomly selected and sequenced.The results showed that β-actin was subtracted significantly at about 2¹⁰ folds,suggested that the subtractive cDNA library was successfully constructed.PCR analysis showed that the inserts were 100-750 bp in length.Based on BLAST searches in NCBI,167 ESTs(40.34%)exhibited homology with genes of known functions,and 7 of the 167 ESTs(1.69%)were possibly related to immune and stress functions,and the remaining 204 ESTs had no significant matches with known sequences in the GenBank database.Altogether,the results obtained from this paper provide valuable information for further investigating the molecular immune mechanism of P.fucata.