The Doppler ultrasound with color flow mapping image has been recently applied for the evaluation of gynecologic diseases, in particular, malignant trophoblastic tumors with the characteristic abundant blood flow. Doppler color flow mapping of uterine artery and intratumoral blood vessels was performed at a regular interval in all 26 patients including 3 cases of lost for follow up. Systolic/diastolic (S/D) ratio representing blood flow was measured in 19 cases of malignant trophoblastic tumors and 7 cases of hydatidiform mole diagnosed at the department of Obstetrics and Gynecology, Yonsei University, College of Medicine. The initial mean S/D ratio and standard deviation(SD) of uterine artery in 11 remitted and 5 non-remitted patients were 2.72 ± 1.31 and 2.69 ± 1.80, respectively. No significant difference was noted between two groups. However, the final S/D ratio of uterine artery in remitted group showed significantly higher values than non-remitted group, of which values were 6.23 ± 2.38 and 3.08 ± 1.54, respectively (p< 0.05). In aspect of blood flow changes in malignant trophoblastic tumors after chemotherapy, remitted group showed entirely disappeared blood flow, while non-remitted group had persistent blood flow. The mean S/D ratio and SD measured in hydatidiform mole patients were 5.43 ± 1.65, of which value reflects higher resistance than malignant trophoblastic tumors. Also blood flow was not detected in all cases. This study suggests that color flow mapping Doppler ultrasound can be a useful method in diagnosing and monitoring the treatment in malignant trophoblastic tumors along with the conventional serum β-hCG titration.