The aim of this study was to determine the effect of continuous intrauterine release of progestin on the uterine artery pulsatility index (PI) in women on postmenopausal hormone replacement therapy (HRT). The voluntary participants, 13 symptomatic postmenopausal women received transdermal estradiol (50 micrograms/day) for 1 month before combining the levonorgestrel-releasing (20 micrograms/day) intrauterine system (LNG-IUS) with estrogen replacement therapy. The PI of uterine artery blood flow was measured by transvaginal color Doppler ultrasonography before the onset of HRT, 1 month after the treatment with estradiol (estradiol-only phase) and 1, 3 and 6 months after insertion of the LNG-IUS. The mean uterine artery PI decreased significantly from its pretreatment level after 1 month of transdermal estradiol treatment (p < 0.05), but the LNG-IUS induced an increase in PI, and 6 months after its insertion the PI did not differ significantly from the pretreatment level (p > 0.05). Compared with the estradiol-only phase, the last measurement of the PI was significantly increased (p < 0.05). The results suggest that continuous intrauterine release of levonorgestrel abolishes the vasodilatory effect on the uterine arteries accomplished by postmenopausal estradiol treatment.