Digital color doppler ultrasonographic system(DCDUS) has a lot of diagnostic functions. One of these is a detection of low velocity vessels in the organs of abdominal cavity. The purpose of study was to determine the clinical usefulness of DCDUS. Interlobar artery resistive index(RI), pulsatility index(PI) and systolic diastolic ratio(SDr) were measured for diagnosis of obstructed urinary tract. RI, PI and SDr were a measure of intrarenal blood flow impedance. This study was consisted of 2 groups. The normal group was studied in 16 normal adult dogs and the study group was studied 7 dogs with surgically induced, unilateral ureateral obstruction. In the study group, parameters were checked in nirmal condition and on 1, 2, 3, 5, 7 and 10th day after ligation. The result were summarized as follows. In the normal group, RI, PI and SDr of the left kidney was 0.65+_0.04, 1.25+_0.12 and 292.45+_29.40, respectively. RI, PI and SDr of the right kidney were 0.64+_0.05, 1.28+_0.20 and 282.25+_37.26, respectively. In the study group, RI of the left kidney induced ligation was increased sighificantly on 1, 2, 3, 5, 7 and 10th day. RI of the left kidney on 1, 2, 3, 5, 7 and 10th day wee 0.75+_0.05, 0.71+_0.03, 0.74+_0.04, 0.74+_0.02, 0.73+_0.02 and 0.73+_0.04, respectively. PI of the left kidney was increased significantly on 1, 3, 5 and 7th day. PI of the left kidney on 1, 3, 5 and 7th day were 1. 57+_0.21, 1.54+_0.24, 1.60+_0.15 and 1.60+_0.26, respectively. SDr of the left kidney increased significantly on 1, 2, 3, 5 and 7th day. SDr of the left kidney on 1, 2, 3, 5 and 7th day were 412.18+_86.69, 352.14+_47.05, 399.77+_65.54, 369.43+_48.34 and 365.57+_22.46, respectively(p0.05). In the study group, RI of the left kidney was more increased than that of the right kidney on 1, 2, 3, 5, 7 and 10th day. PI of the left kidney was more increased than that of the right kidney on 1, 3, 5, and 7th day. SDr of the left kidney was more increased than that of the right kidney on 1, 2, 3, 5 and 7th day(p0.05). RI was effective in the diagnosis of an acute unilateral ureteral obstruction. PI and SDr were insufficient in the diagnosis of an acute unilateral ureteral obstruction.