Objective The estrogen receptor (ER) is a transcription factor that mediates the function of the hormone estrogen in many physiological and pathological processes. The expression of the estrogen receptor (ESR1), which encodes the alpha estrogen receptor (ER-α ), is tissue specific. For example, the expression of ESR1 in the endometrium and mammary gland is very high and low in the placenta and skin. The gene is located on human chromosome 6 and is also known as Era, ESRA, ESTRR, and NR3A1. Several studies have shown that genetic variants in this gene are associated with breast cancer sensitivity. The aim of this study was to investigate ESR1gene expression in different tissues of Raini Cashmere goat using Real Time PCR. Materials and Methods One male and one female goats were selected for tissue sampling. Samples were taken from tissues of the heart, kidneys, brain, ovaries, uterus, breast and testicles (3 repetitions of each tissue) during slaughter at the slaughterhouse. RNA was extracted and cDNA was synthesized. Real Time PCR was performed using SYBR Green method to study relative gene expression. GAPDH gene was used as housekeeping gene. Pfaffl method was used to analyze achieved data. Results The study of ESR1 gene expression in the tissues of the heart, kidney, brain, ovary, uterus, mammary gland and testis of goat using Real Time PCR showed that this gene is expressed in all studied tissues. The highest levels of expression were observed in the kidney, ovary, uterus and testis tissues, and the lowest levels of expression were observed in the brain and heart tissues. Conclusions Based on the results of the present study and the results of other researchers, it can be concluded that estrogen receptors play an important role in spermatogenesis and male fertility, because in the present study it was found that ESR1 is much more expressed in reproductive tissues than in non-reproductive tissues. Therefore, estrogen and its receptors are likely to be essential for male fertility, and the results of this study provide a basis for future research to describe the role of ESR1 gene as a candidate gene for better fertility and natural physiology in domestic animals, especially goats.