The androgen receptor (AR) is a ligand-activated transcription factor of the male and female reproductive tracts whose activity is modulated by coregulator binding. We recently identified melanoma antigen gene protein-11 (MAGE-11) of the MAGEA gene family that functions as an AR coregulator by binding the AR N-terminal FXXLF motif. Here we report that MAGE-11 is expressed in a temporal fashion in endometrium of normally cycling women. Highest levels of MAGE-11 mRNA and protein occur in the mid-secretory stage, coincident with the window of uterine receptivity to embryo implantation. Studies in human endometrial cell lines together with the hormone profile of the menstrual cycle and pattern of estrogen receptor-alpha expression in cycling endometrium suggest the rise in MAGE-11 mRNA results from down-regulation by estradiol during the proliferative phase and up-regulation by cyclic AMP signaling in the early and mid-secretory stage. In agreement with its coregulatory function, MAGE-11 localizes with AR in glandular epithelial cell nuclei in the mid-secretory stage. The increase in AR protein in the mid-secretory endometrium without an increase in AR mRNA suggests MAGE-11 stabilizes AR in glandular epithelial cell nuclei. This was supported by expression studies at low androgen levels indicating AR stabilization by MAGE-11 dependent on the AR N-terminal transactivation domain. The results suggest that MAGE-11 functions as a coregulator that increases AR transcriptional activity during the establishment of uterine receptivity in the human female.