Oncostatin M (OSM) is a member of the interleukin-6 (IL-6) family, which functions in embryo implantation and decidualization. The expression, function and regulation of Osm in mouse uteri during early pregnancy remain unknown. We show that Osm is mainly expressed in the uterine epithelium from days 1 to 4 of pregnancy and in decidual cells on day 5 of pregnancy. Osm promotes the attachment of Osm-soaked blue beads, which mimic blastocysts, to a pseudopregnant mouse uterus. Prostaglandin E2 (PGE2 )-induced Osm in mouse uterine epithelial cells upregulates the levels of Il-33 expression and phosphorylates Stat3. In vitro decidualization is significantly promoted by Osm. Our results indicate that PGE2 -induced Osm may mediate embryo implantation through Il-33 and participate in decidualization via the Stat3-Egr1 pathway.