Background: Chicken Ovalbumin Upstream Promoter-Transcription Factor I (COUP-TFI) is a member of the steroid/thyroid nuclear receptor superfamily. The aim of this study was to investigate whether absence of this gene affects placental development and fetal growth in a COUP-TFI knockout mouse model. Methods: Placentas of COUP-TFI-knockout (COUP-TFI KO) and wild-type (WT) were collected at 18.5 days post-coitum. The expression level of the following genes known to be involved in different key molecular pathways was evaluated: BCL2 Associated X (Bax) and B-cell lymphoma 2 (Bcl-2) (apoptosis), p21, p53 and \alpha subunit of inhibin (INHA) (proliferation and apoptosis), vascular endothelial growth factor A (VEGF-A), placental growth factor (PlGF), hypoxia-inducible factor 1-alpha (HIF1\alpha), Fms related receptor tyrosine kinase 1 (Flt-1), and endoglin (ENG) (angiogenesis). Mouse litter weight at birth was also assessed. Results: RT-qPCR analysis showed increased mRNA expression of VEGF-A and Bax in placental tissue of COUP-TFI KO mice compared to WT mice. We also found a loss in the positive correlation between Bcl-2 and INHA, p21 and ENG, as well as HIF1\alpha and Flt-1 mRNA expression in COUP-TFI mutants. Finally, KO mice were lighter than WT littermates (respectively, the mean weight of COUP-TFI KO mice was 1.3 grams, \pm 0.13, compared to 1.6 g, \pm 0.14 of WT mice, p 0.05). Conclusions: Our results show that COUP-TFI deletion is associated with a lower birth weight in mice and increased placental transcript expression of pro-apoptotic Bax and pro-angiogenetic VEGF-A genes.