As a kind of transcription factors, MADS-box protein plays an important role in various cellular processes, especially in the development of floral organs. Based on the contig analysis of the cotton ESTs, the coding region of a cotton MADS-box protein (GhMADS1) was obtained by RT-PCR from floral buds of cotton (G. hirsutum). The cloned fragment of 713 bp (GhMADS1, GenBank accession no. AF538965) contains an open reading frame of 711 bp,coding a polypeptide of 236 amino acids. It was demonstrated that the deduced GhMADS1 protein was highly homologous to the AGL2 group of MADS-box proteins from Vitis vinifera, Nicotiana sylvestris, Petunia hybrida, Arabidopsis thaliana and Antirrhinum majus. Phylogenetic analysis also indicated that GhMADS1 belongs to the AGL2 group of MADS-box proteins. RT-PCR analysis showed that GhMADS1 gene expressed in petals, stamens, ovules and fibers, but not in roots, stems, leaves, bracts and sepals. The strongest expression of GhMADS1 gene was detected in petals. But in floral buds of a cotton homeotic mutant (CHV1), whose floral organs are all converted to bract leaf-like organs, the transcript of GhMADS1 gene was not detected. It was proposed that GhMADS1 gene would be crucial to the development of cotton floral organs.