The full-length cDNA sequence of tributyltin-binding protein type1 in Japanese medaka (Oryzias latipes) (Olat.TBT-bp1) was determined by means of rapid amplification of cDNA ends (RACE) of liver tissue. Analysis of the structure of the gene encoding Olat.TBT-bp1 revealed that the exonintron organization of this gene corresponds to that of the genes encoding lipocalin superfamily proteins, suggesting that Olat.TBT-bp1 can be categorized as a member of the lipocalin superfamily, which may play an important role in transportation, detoxification, and excretion of xenobiotic compounds. Reverse transcription — PCR revealed that Olat.TBT-bp1 was expressed mainly in the liver, and upregulation of its expression was detected 1, 2, and 4 weeks post hatching. Relative expression of the Olat.TBT-bp1 gene was significantly downregulated, compared with that in the solvent control, by exposure to tributyltin at 0.01 mg/l or triclosan at 1.7 mg/l. Further studies on Olat.TBT-bp1 expression in conjunction with other biochemical and physiological toxicities in response to chemical exposures are needed to increase our understanding and information of TBT-bps mechanisms and as molecular biomarkers of chemical exposures. The role of Olat.TBT-bp1 in xenobiotic detoxification and/or excretion needs more investigations.