Pregnancy is characterised by profound changes in maternal physiology. For instance, there are changes in the metabolic, cardiovascular, immune and renal systems of the mother which enable her to support fetal nutrient supply and growth. These changes are signalled in part by the production of protein hormones by the placenta (Napso et al., 2018). Failures in maternal adaptation and placental function lead to pregnancy complications such as abnormal birth weight and gestational diabetes. However, we lack information on the identity of hormones secreted by the placenta that mediate the changes in maternal physiology. This study aimed to identify the protein hormones expressed by endocrine cells in the mouse placenta. Primary cell cultures of the whole placenta from mouse dams on day 16 of gestation were established (term=20 days). Proteins in the conditioned media (serum-free) at 48 h of culture were identified by LCMS. In parallel, endocrine cells were sorted from whole placentas of mice on day 16 of pregnancy using fluorescence-activated cell sorting. Peptides expressed by placental endocrine cell isolates were identified by LCMS. Protein IDs were converted to gene lists using accession ID. Gene lists were overlaid with published mouse and human placental RNA-seq data (n=3 and n=6, respectively). We identified a total of 1195 proteins in mouse placental endocrine cell isolates and secretomes (85% overlap between two types of samples), of which 34% are known to be secreted. Gene ontology identified that placental endocrine cell proteins have proposed roles in metabolic regulation, immune modulation, signalling and growth. Most proteins/genes have homologues expressed by the human placenta and several are reported to be dysregulated in women with pregnancy complications like abnormal birthweight and gestational diabetes. Work is currently underway to assess whether secreted placental proteins could serve as diagnostic indicators for human pregnancy complications.