Transcription factors (TFs) are the key regulators of gene expression and play crucial roles during plant growth and development. A novel TF family, containing one or two BSD domains in a variety of organisms ranging from prokaryotes to human, was newly identified by computational analysis. In this study, one Arabidopsis gene encoding the BSD domain, designated as AtBSD1, was characterized. The AtBSD1 transcript was expressed in all Arabidopsis tissues tested. The expression level of the AtBSD1 transcripts was not controlled by exogenous application of abiotic stresses and plant hormones. When the AtBSD1::GFP construct under the control of the CaMV35S promoter was introduced into onion epidermal cells, a GFP signal was detected in the nucleus. A transcriptional activity assay of the AtBSD1 protein in yeast revealed that the AtBSD1 protein functions as a transcriptional activator, and the N-terminal region (1-204 amino acids) of the AtBSD1 protein contains a transcriptional activation domain. These results suggest that Arabidopsis genes encoding the BSD1 domain might be classified as a novel transcription factor family.