In primates, a cyclic physiological changes oocurs inside the female reproductive tract, termed as menstrual cycle. The whole cycle takes 28 days approximately to complete. The end of the cycle occurs with the breakdown of uterine endothelium wall that releases in the form of blood and mucus through the vagina and is termed as menses. Various hormones play their role in menstrual cycle namely follicle stimulating hormone (FSH), luteinizing hormone (LT), estrogen and progesterone. The level of FSH and LT increases during the follicular phase and are secreted by anterior pituitary gland. FSH stimulates the conversion of primary follicle into Graafian follicle under the influence of RH (releasing hormone) from the hypothalamus. Increase in LH level gradually leads to the growth of follicle and secretion of estrogen, then estrogen inhibits secretion of FSH but stimulates LH and also causes the thickening of uterine endometrium. High level of LH causes Graafian follicle to rupture and release ovum into the fallopian tube. This ruptured graafian follicle converts to corpus luteum and secretes progesterone hormone during the luteal phase. Maintenance and preparation of endometrium for the implantation of embryo is done by progesterone and increased level of this hormone in blood decreases the secretion of LH and FSH, thus inhibiting further ovulation.