Background The administration of steroids is not always effective for the treatment of ulcerative colitis (UC). Their long-term use often causes adverse effects which sometimes result in their stoppage and acute exacerbation. Therefore, an alternative treatment is necessary in order to decrease steroid dosage and avoid the clinical problems associated with steroids. Methods The effectiveness and adverse effects of a leukocytapheresis (LCAP) were investigated in a controlled multicenter trial with randomized assignment of 76 active-stage UC patients in two groups. In the LCAP group (39 patients), LCAP weekly for 5 weeks as an intensive therapy was added to the on-going drug therapy, while steroids were maintained but not increased, and then LCAP was gradually reduced to once every 4 weeks as a maintenance therapy. In the high dose prednisolone (h-PSL) group (37 patients), PSL was added or increased 30∼40 mg / day for moderately severe and 60∼80 mg / day for severe patients and then gradually tapered. Findings The LCAP group showed a significantly higher effectiveness (74% vs. 38%, p=0.005) and lower incidence of adverse effects (24% vs. 68%, p < 0.001). The patients were able to continue the trial for a longer period in the LCAP group than the h-PSL group (p=0.012). Clinical activity and endoscopic indexes showed the LCAP group had better improvements than the h-PSL group. Interpretation The results of the trial show that LCAP permits a reduction in total PSL dosage and is more effective and safer than high-dose PSL administration for intensive therapy, and LCAP may maintain remission longer than PSL.