RB1-inducible coiled-coil 1 (RB1CC1) is a novel molecule implicated in the regulation of RB1 (retinoblastoma 1) expression. However, information about the RB1CC1 gene is limited and its function remains somewhat obscure. The present study analyzes the expression and promoter activities of RB1CC1 in developing murine and human tissues. Rb1cc1 was abundantly expressed from an early stage of the mouse embryo throughout development. Immunohistochemical analyses revealed that Rb1cc1 was ubiquitous in the mouse, rather than in the human embryo, especially in the musculoskeletal system, heart and neural tissues. Promoter activity was highest in a region located about 300 bp immediately upstream of exon 1 in both the mouse and human RB1CC1 genes, suggesting that this region is a core promoter. The promoter activity of RB1CC1 was generally higher in mice than in humans, and suppressive with intron 1, especially in humans. These results suggested that more Rb1cc1 is expressed throughout developing murine than in human tissues, and that RB1CC1 expression is controlled more stringently by modification at intron 1 in humans than in mice.