The feline Fas ligand gene was molecularly cloned from a feline genomic library and its genomic organization was determined. The feline Fas ligand gene contained four exons and spanned approximately 10 kb in the genome, and thus had the same structure as the human Fas ligand gene. The promoter region of the feline Fas ligand gene was further characterized by deletion mapping. The region between nucleotides -459 and -172 relative to the ATG codon was essential for the promoter activity when transfected into human and feline lymphoid cells. The characterization of the feline Fas ligand gene in the present study will be useful for further investigations of the regulatory mechanism of feline Fas ligand expression.