Hox genes in mammals are the homogenetic genes of homeotic selector genes (HOM genes) in Drosophila. These genes include an encoding sequence of 183 bp, which encode a conservative protein domain of 61 amino acids. Both the nucleotide sequence of Hox gene and their position on the chromosomes are highly conservative. Hox genes are important in the regulation of spatial information during development, such as the differentiation of somites. Each somite acquires its own specialty according to its singular spatial position. Recent studies suggest that Hox genes not only influence embryonic development, but also have effects on the differentiation of adult reproductive system. They play an indispensable role in the establishment of uterine receptivity and the decidualization.