Adenylosuccinate lyase (ADSL) is a bifunctional enzyme acting in de novo purine synthesis and purine nucleotide recycling. In the present study, we have constructed a grass carp (Ctenopharyngodon idella) intestinal cDNA library that has over 2.3 × 10(5) primary clones. An expressed sequence tag (EST) of grass carp adenylosuccinate lyase (gcADSL) gene was screened from this library. Both 5'-RACE and 3'-RACE were carried out in order to obtain the complete cDNA sequence, which contains a 1,446 bp open reading frame encoding 482 amino acids about 54.552 kDa. The deduced amino acid sequence shares high homology with its vertebrate counterparts, which shares 94% similarity with zebrafish, 81% with African clawed frog as well as chicken, 77% with human and 76% with mouse. This gcADSL genomic sequence, consisted of 13 exons and 12 introns, is 8,557 bp in size. Real-time quantitative PCR analysis revealed that the highest expression level of gcADSL was detected in muscle and the lowest in gill. In western blotting analysis, His(6)-tagged gcADSL protein expressed in Escherichia coli could be recognized not only by an anti-His(6)-tag monoclonal antibody but also by an anti-human ADSL polyclonal antibody, indicating immunological crossreactivity occurs between grass carp and human ADSL protein. 1,082 bp 5'-flanking region sequence was cloned and analyzed.