Flower development is regulated by a group of regulatory factors containing the MADS box domain. Recently, we isolated and characterized a tobacco MADS-box gene, NtMADS1, which is homologous to AGL2 in Arabidopsis. Sequence analysis revealed that NtMADS1 encodes a putative MADS-box protein homologous to the AGL2 with 68.4% identity and 82% similarity in amino acids. The NtMADS1 gene started to express at a very early stage of flower development, such as floral primodia, and the expression was maintained during the entire floral development. In the tobacco flower, the gene was expressed in all four floral organs, namely the sepal, petal, anther, and carpel, and was not detected in the vegetative organs such as the leaf and root. In situ hybridization was also performed to monitor the detailed expression pattern of NtMADS1 at the tissue level. These results indicate that NtMADS1 is the AGL2 homolog of tobacco and plays important roles in the floral development.