Decidualization is a process characterized by morphological and functional changes in the uterine stromal cells. In addition to steroid hormones, growth factors are implicated in this process. Using in situ hybridization, we found that mRNAs for several bone morphogenetic proteins (BMPs) were detected in the decidual and vascular endothelial cells. The Bmp7 mRNA was detected in the decidualizing stromal cells surrounding the blastocyst and distributed in a gradient, with the highest levels occurring near the uterine epithelium at 4.5 days post-coitus (dpc). With the progression of decidualization, Bmp7 signals in the deciduum at the antimesometrial side decreased, but strong signals were retained in the decidual area at the mesometrial side at 7.0 dpc. In contrast, Bmp8a transcripts increased from 5.5 to 7.0 dpc in the decidual tissue, with the highest levels occurring in the secondary decidual zone at the antimesometrial side. The Bmp2, Bmp4, and Smad1 transcripts were found in the secondary decidual zone, especially at the mesometrial side. The Bmp2 signals were primarily detected in decidual cells, whereas Bmp4 and Smad1 transcripts were mainly detected in vascular endothelial cells, suggesting that they may be involved in decidual angiogenesis.