In this study, the cytochrome P450 3A (CYP3A) gene was cloned from the turbot Scophthalmus maximus for the first time using reverse transcription-polymerase chain reaction (RT-PCR) and rapid amplification of cDNA ends approaches. The amino acid sequences were analyzed with corresponding software programs. The cDNA of CYP3A was 1,969 bp in length, which contained a 5'-untranslated region (UTR) of 34 bp, a 3'-UTR of 404 bp and an open reading frame of 1,530 bp encoding a predicted protein of 509 amino acids (GenBank accession No. JN216889). The deduced protein had a molecular weight of 58.09 kDa and an isoelectric point of 5.75. Amino acid sequence alignment indicated that turbot CYP3A shared 60-67% homology with other fish species. It consists of a signal peptide, six conservative substrate recognition sites (SRS 1-6) and the conserved heme-binding motif FXXGXXXCXG in all CYP3As. Quantitative real-time RT-PCR analysis indicated that turbot CYP3A mRNA was widely expressed in liver, kidney, gill, muscle, stomach, intestine, gallbladder and spleen, with the highest level in liver and the lowest in muscle. After oral administration of sulfamethazine, CYP3A expression in all experimental groups enhanced compared with control, and the expression varied with administration time. It suggested that CYP3A expression could be induced by sulfamethazine. Our findings provided molecular characterization and expression profile of turbot CYP3A, and revealed the important role that turbot CYP3A played in drug metabolisms.