LIM-homeodomain transcription factors control a wide range of developmental processes, such as early patterning of the embryonic development, organ formations of brain, limbs, and eyes. Molecular mechanisms of the underlying processes involve complicated multiple protein complexes that direct transcription activation of target genes, protein-protein interactions, and transcriptional regulations. Among those molecules, cofactor Ldb1, interacting with LIM/homeobox family transcription factor, defines a tetrameric protein complex in controlling downstream genes of transcriptional regulation. In addition, SSDP specifically involves this complex supported by showing that both SSDP1 and SSDP2 bind to Ldb1 in vivo. Here it has been found that SSDP1 itself is a transcription factor that has transcription activity independently. Furthermore, C-terminal of SSDP1 possessing an entire transcription activity in vivo, confirmed in both yeast and mammalian cells, has been defined. Interestingly, the transcriptional function of SSDP1 was not required for the interaction with Ldb1. Thus, biochemical data of SSDP1 presented by this study provides biochemical evidence for a better understanding of transcriptional regulation.