Estrogen mediates growth, differentiation, and function of tissues of the uterus.The response of the uterine epithelium to estrogen provides an excellent model to study cell proliferation. Estrogen treatment stimulates endometrial cell proliferation and the enlargement of the immature rat uterus. In contrast, Tamoxifen has agonist and antagonist effect in the uterus; however, Tamoxifen has principally antagonistic effects in breast tissues. The present study identified gene transcripts with potentially important regulatory roles and biomarkers for estrogen and Tamoxifen action.Identification of specific estrogen and Tamoxifen regulating oligonucleotides for induced or repressed markers could provide essential information on molecular events regulating proliferation and differentiation responses to estrogen and its antagonist Tamoxifen.