The aim of this study was to determine whether there is a difference in pregnancy outcomes dependent on the kind of hormone replacement treatment in the luteal phase after transfer of frozen-thawed embryos in the natural ovulation cycle. Two hundred and twenty-three cycles were examined in this study. The cycles were divided into three groups. In group A (40 cycles), the luteal phase was supported by human chorionic gonadotropin (hCG). In group B (83 cycles), the luteal phase was supported by hCG and vaginal suppository of progesterone. In group C (100 cycles), the luteal phase was supported by hCG, vaginal progesterone and transdermal estradiol. The pregnancy rate and implantation rate in group C (63.0% and 44.3%) were significantly and 28.0%) and group B (45.8% and 30.3%). In conclusion, administration of vaginal progesterone and transdermal estradiol in addition to hCG in the luteal phase in the natural ovulation cycle is effective for improving pregnancy and implantation rates in patients undergoing transfer of frozen-thawed embryos.