Purpose Cinematic rendering (CR) is a new technique for visualizing volumetric three-dimensional data. The purpose of this study was to investigate the added value of CR to conventional computed tomography (CT) in the diagnosis and evaluation of ulcerative colitis (UC). Materials and methods We retrospectively evaluated the CT data of 48 patients (33 men, 15 women; mean age, 44.35 years) with a definitive diagnosis of UC. All patients underwent conventional CT and CR, and had colonoscopy results. Two radiologists independently reviewed the conventional CT images first without and then with CR. Then, the imaging value of CR was evaluated by both radiologists together. The readers were blinded to the disease extent. The diagnostic performance of CR for both readers was assessed by receiver-operating characteristic (ROC) curve analysis. Results There were 23 cases of mild to moderate UC and 25 cases of severe UC, which were divided into two groups. Both readers showed improved diagnostic performance with the addition of CR (the area under the ROC curve improved from 0.676 to 0.804, P=0.0255, and from 0.679 to 0.826, P=0.0049, for readers 1 and 2, respectively). Full view of the lesion and contrast enhancement was not significantly different between the two groups (P>0.05). Increased mesenteric vascularity and the comb sign on CR were more clearly observed in the severe group (P<0.05). Conclusion Adding CR to conventional CT improved the diagnostic performance of evaluating the extent of UC.