Purpose: Relationship of apparent diffusion coefficient (ADC) values of colonic wall and pathologic pericolonic lymph nodes with inflammatory activity in ulcerative colitis patients is investigated by the use of diffusion-weighted magnetic resonance imaging (DW-MRI). Materials and Methods: A total of 28 ulcerative colitis patients -9 endoscopically active, 10 subacute and 9 in remission- were evaluated with DW-MRI with 0, 500 and 1000 s/mm2 b values. The ADC values of rectum and sigmoid colon walls and adjacent pathologic pericolonic lymph nodes were measured for quantitative analysis. The DW-MRI findings were compared with disease activity. Results: ADC levels of sigmoid colon were similar among active, subacute and in remission patients (p: 0.472). ADC levels of rectum were different (p=0.009) among patients in active phase (1.08 ± 0.14 x10ˉ³ mm²/s), subacute phase (1.13 ± 0.23 x10ˉ³ mm²/s) and in remission (1.29 ± 0.17 x10ˉ³ mm²/s). The ADC values of pericolonic lymph nodes (p=0.899), were not different with respect to disease activity. Conclusion: DW-MRI seems to be useful to identify the disease activity among ulcerative colitis patients especially in rectum. Rectum ADC values increase in remission and decrease in active distal colitis. ADC values of pericolonic lymph nodes did not help to differentiate the disease activity.