The objective of this review is to uncover the activity of oxytocin in various biological systems in the body related to reproductive functions. Oxytocin is a peptide hormone produced in the brain, storage, and secretion from the pituitary gland in most animals especially the mammals. Oxytocin was discovered at first time by Henry Dale in 1906. Whereas, its structure was discovered in 1952. Oxytocin has a wide variety of physiological functions such as milk removal, maternal behavior, cancer and sexual behavior in both type sex (male and female), for example, its play a role in excitation penile, ejaculation, accessory glands performance and the contractions of smooth muscles of the uterus and pelvic during mating and parturition, growth and development of the corpus luteum and progesterone level in blood. Also, oxytocin effect on some hormones such as prolactin and luteinizing hormone. Furthermore, there is a relationship between oxytocin and stress tolerance. So, understanding the effects of oxytocin on somebody's functions is important and necessary to provide information about body biological processes which control by this hormone.