Galectins are a family of β-galactoside-binding lectins which play crucial roles in innate immunity of vertebrates and invertebrates. In the present study, we have cloned and characterized the first galectin to be identified in Tegillarca granosa (designated Tg-GAL). The full-length cDNA of Tg-GAL was of 2,394 bp nucleotides, encoding a polypeptide of 354 amino acids. The amino acid sequence of T. granosa galectin (Tg-GAL) showed striking sequence similarity to invertebrate and vertebrate galectins in carbohydrate recognition domains (CRD) and contained amino acids that are crucial for binding β-galactoside sugars. Structurally, the Tg-GAL was a tandem repeat galectin containing two CRD connected by a unique peptide link. Quantitative real-time PCR was employed to investigate the tissue distribution of Tg-GAL mRNA and temporal expression in haemocytes of clams challenged with Vibrio parahaemolyticus, lipopolysaccharide (LPS) and peptidogylcan (PGN). The Tg-GAL mRAN expression was concentrated in hepatopancreas and mantle. The up-regulation of Tg-GAL after bacteria V. parahaemolyticus, LPS and PGN challenge showed that Tg-GAL might play a pivotal role in anti-bacterial immunity. Further study should investigate the effects of Tg-GAL absence by siRNA knockout.