Seminal fluid induces major changes in the female reproductive tract to initiate maternal immune tolerance for embryo implantation and placental development. The full extent of immune cell changes and their contribution to endometrial receptivity is not fully defined. RNA-sequencing has revealed that T cell recruitment is amongst the top biological pathways induced in the endometrium by seminal fluid in mice1. Genes associated with gamma/delta (γδ) T cells were dominant amongst the differentially regulated genes, including γδ TCR genes Trdc and Tcrg-C1 (2.0- and 2.5-fold increase) and γδ T cell function genes Il7r and Blk (2.5- and 2.8-fold increase). Therefore, we sought to test the hypothesis that seminal fluid contact elicits changes in uterine γδ T cell populations. To assess this, we utilised flow cytometry to quantify and phenotype γδ T cells in the endometrium and uterine-draining lymph nodes on day 3.5 post-coitum (pc) after mating with intact (INT), vasectomised (VAS), seminal vesicle-deficient (SVX), and SVX/VAS BALB/c males, as well as virgin estrous females (n=11-12/group). The γδ T cell population in the uterus was dramatically expanded after INT or VAS mating by 8.3-and 10-fold compared to estrous females, with 22.4- and 21.9-fold more γδ T cells expressing proliferation marker Ki67. Similar increases in γδ T cells were seen in draining lymph nodes. The increase did not occur after mating with SVX or SVX/VAS males, consistent with the gene expression changes that depended on seminal plasma. These findings demonstrate that expansion of a resident γδ T cell population is a major but hitherto unidentified element of the uterine immune response regulated by seminal fluid. Given the central roles of γδ T cells in epithelial homeostasis in other mucosal surfaces, this response may modulate receptivity to embryo implantation - but future studies are required to define its exact contribution to reproductive success.