Luteal phase defect (LPD) is an ovulatory disorder of considerable clinical importance that leads to delayed endometrial maturation and inadequate endometrium for blastocyst implantation. This disorder is implicated in infertility and recurrent spontaneous abortion. We analyzed the endometrial histological maturation, and the estrogen receptor(ER) and progesterone receptor(PR) status in patients with unexplained delayed ovulation, and in patients with ovulation induction by clomiphen citrate. The purpose of this study was to determine whether the length of the follicular phase influences the endometrial histological maturation and the hormonal receptor status, and to know the effect of clomiphen citrate on the endometrium. In the delayed ovulation group, the endometrium was characterized by an irregular outpouching and dilated lumina of the glands, a decreased secretory activity and predecidualization, and a decreased number of granulocytes in the stroma. In the clomiphen citrate-ovulation induction group, glandular proliferation was markedly diminished with poorly convoluted and narrow glands, secretory activity was decreased, stroma was undecidualized, and there was an absence of granulocytes. ER expression was increased in the glandular epithelium in the delayed ovulation group, and both ER and PR expressions were markedly decreased in the glandular epithelium and stromal cells in the ovulation induction group. Endometrial maturation and differentiation may be diminished by increased estrogenic and relatively deficient progesterone effects in patients with delayed ovulation. The hormonal receptor status might also be influenced by hormonal changes. Clomiphen citrate successfully induced ovulation in patients with delayed ovulation, however, endometrial proliferation and maturation were markedly suppressed. This might be related to the lower pregnancy rate and higher abortion rate in patients with clomiphen citrate induced ovulation.