AbstractUterine natural killer (uNK) cells are the dominant lymphocytes of pregnant mammals' uterus. Studies have identified four differentiation stage of mouse uNK cells based on Dolichos biflorus lectin cytochemistry, and their distribution showed preferential domain in the uterus through out the pregnancy. This work was done to investigate the expression of α5, α6, and β7 integrins on uNK cells and their ligands distribution. Section of mouse uterus from sixth to seventeenth gestational days were submitted to immunocytochemistry and positive reactions for α5, α6, and β7 integrins were found on uNK from eighth to tenth gestational days but not after twelfth gestational days. Fibronectin reactions were seemed from sixth to tenth gestational days around uNK from the myometrium and endometrium close to the myometrium. No reaction for fibronectin was seen in the decidualized and nondecidualized endometrium near the placenta. Laminin reaction was seen just in the antimesometrial side. β7 integrin seems to be the active receptor to bind with VCAM‐1 or MAdCAM‐1 of endothelial cells, promoting the uNK cross through the vessels. The absence of laminin in an uNK domain suggests these cells are not dependent of laminin and α6 integrin for their establishment. However, fibronectin seems to support uNK migration, proliferation, differentiation, and survival in the uterus by binding with α5 integrin. The loss of α5 integrin ligation by the down regulation of fibronectin could inhibits these events and further studies are need to investigate whether unligated α5 can actively and initiate apoptosis, maybe in a caspase 8‐dependent way that has been called integrin‐mediated death. Anat Rec, 2010. © 2010 Wiley‐Liss, Inc.