Seminal fluid interacts with epithelial cells lining the female reproductive tract to induce pro-inflammatory cytokines and chemokines, which in turn initiate immunological adaptations required for pregnancy. Factors in the seminal plasma fraction including TGFB are identified as key signalling agents, but don’t fully account for the female response, since our recent studies show differential gene expression in the female when sperm is present in the ejaculate. Various candidate bioactive molecules in sperm may mediate this response, including microRNAs (miRNA). We hypothesised that sperm-borne miRNA contributes to regulating gene expression in the female following insemination. CBAF1 female mice were mated with intact or vasectomised Balb/c males, sacrificed 8h later and compared with unmated estrous mice. miRNA and RNA expression profiles in endometrial tissue were examined by Affymetrix microarray. Thirty-four miRNAs were differentially regulated (>1.5 fold) in the endometrium of mice mated with intact males compared to vasectomised males. Of these, mir-223 and mir-146a which are known regulators of inflammation and immunity were studied further. PCR showed mir-223 and mir-146a increased 3.38-fold and 1.94-fold respectively in the endometrium after intact compared to vasectomised mating. Consistent with a possible origin in sperm taken up by endometrial tissue, both mir-223 and mir-146a were present in cauda epididymal sperm purified from C57Bl/6 mice, and in situ hybridization analysis of mir-223 revealed a punctuate pattern in epithelial and occasional stromal cells of mated but not unmated mice. Immune regulatory genes that are predicted targets of mir-223 (Acvr2a, Nfat5 and Zxdc) and mir-146a (Erbb4) were decreased in the endometrium after intact compared to vasectomised mating. These data suggest that sperm-borne miRNAs are transmitted to the female reproductive tract after coitus to act as novel regulators of the immune response. Future studies will use miRNA knockout mice to elucidate the roles of these miRNAs during the peri-conceptual period.