Abstract: To investigate localization and quantum of ERα mRNA in ovary and uterus of porcine on D 2, 7, 12, 17 throughout menstrual cycle, nonradioactive in situ hybridization using oligonucleotide probes labeled by DIG was applied In the porcine ovary, positive signals for ERα mRNA were limited exclusively to the granulose cells of all types of follicles and were present in a few cells of early corpora lutea. Level of ERα mRNA in ovary remained low during the whole oestrus cycle but increased during proestrus on D 17. ERα mRNA positive signals were mainly detected in glandular epithelial cells and a few of stroma cells in the uterus Abundance of ERα mRNA in porcine endometrium on D 17 was significantly higher than that of D 12 (P<0.01). E₂ concentrations of serum on D 2, 7, 12, 17 during the menstrual cycle were measured by radioimmunoassay. The levels of ERα mRNA in porcine endometrium synchronized the changes of estrogen with positively relations (r=0.918).