Colonoscopies can predict long-term prognoses in patients with ulcerative colitis (UC). Recently, a new imaging technology has been developed that uses 3 types of illumination with center wavelengths of 540 nm, 600 nm, and 630 nm. The use of both the 600-nm and 630-nm lights (Dual red imaging; DRI) is critical for identifying blood vessels in deeper tissue. The aim of this study was to evaluate the usefulness of DRI for assessing the severity of inflammation in patients with UC.  A total of 43 UC patients were retrospectively enrolled to evaluate the endoscopic severity of 112 colon segments, and Mayo endoscopic scores, DRI scores and the severity of inflammation on a visual analogue scale (VAS) were compared. The Mayo endoscopic scores, DRI scores, and histologic scores were evaluated, and the interobserver agreement on DRI scores among 5 investigators was also assessed. The usefulness of DRI scores for predicting prognoses was also assessed in patients with clinical remission.  The DRI scores were closely correlated with the VAS for the severity of colonic inflammation (r = 0.96) and the histologic scores (r = 0.72 - 0.8). The DRI scores had a higher rate of interobserver agreement (κ values = 0.63 - 0.88) than the Mayo endoscopic scores (κ values = 0.44 - 0.59). Inter-observer agreement between 4 non-experts was also excellent (mean κ value = 0.76, range 0.63 - 0.82). The expected time until recurrence was significantly longer in patients with lower DRI scores ( < 0.01).  DRI can be used in patients with mild to moderate endoscopic severity because it targets the deep vascular pattern. The prognosis of UC can be predicted by assessing deep vessels using DRI.