Human ST7R (ST7-like, ST7L) is a paralog of tumor suppressor gene ST7 in the human genome. ST7R gene is clustered with WNT2B gene in human chromosome 1p13, while ST7 gene is clustered with WNT2 gene in human chromosome 7q31. Here, we have cloned mouse ortholog of human ST7R using bioinformatics and cDNA-PCR. Mouse St7r was found to encode 559 amino-acid polypeptide. Mouse St7r showed 90.7% total-amino-acid identity with human ST7R isoform 4 (ST7R4), and 71.6% total-amino-acid identity with human ST7 and mouse St7. Three tyrosine-phosphorylation sites as well as ST7R homologous domains (S7H1, S7H2, and S7H3) were conserved among mouse St7r, human ST7R, mouse St7, and human ST7. Leucine zipper domain of mouse St7r was conserved in human ST7R, but not in mouse St7 and human ST7. Mouse St7r was expressed almost ubiquitously in adult mouse tissues and also in mouse embryos. Although mouse genome draft sequence including mouse St7r gene has not yet been identified, rat genome draft sequence AC106372.1 was found to include rat St7r gene as well as rat Wnt2b gene. These results indicate evolutional conservation of ST7R-WNT2B gene cluster. This is the first report on molecular cloning and initial characterization of mouse St7r.