We used color Doppler ultrasonography (US) to evaluate bowel wall thickening in ulcerative colitis and to determine the value of this modality in this application. Twelve patients (6 men and 6 women) with ulcerative colitis underwent both gray-scale and color Doppler US. Bowel wall thickness and wall echotexture were recorded by gray-scale US, and the presence of intramural color Doppler flow and arterial signal were evaluated by color Doppler US. Color Doppler flow was graded as 'weak' or 'abundant', and resistive index was calculated; clinical severity of disease activity was also graded, and serum CRP level was measured. Variation in serum CRP levels and intramural color Doppler flow according to clinical severity, and the correlations between serum CRP levels and the number of blood flow signals were statistically significant. In 10 of the 12 patients, analysis of the Doppler waveform showed an arterial blood flow signal, and mean resistive index value was determined to be 0.550. We thus conclude that information provided by gray-scale and color Doppler US is useful in evaluating bowel wall thickening in ulcerative colitis.