Leukocytapheresis (LCAP) has been advocated as a treatment for moderate to severe active ulcerative colitis (UC) in Japan. To clarify the predictive factors for a rapid response to LCAP treatment, we conducted a multicenter prospective open-label study. A total of 105 patients with UC were analyzed. LCAP was performed using a Cellsorba EX column once a week for 5–10 sessions. The response was evaluated by the clinical activity index (CAI). When the CAI score decreased to less than half the pretreatment value or to less than 5 points within 3 weeks, the patient was considered to be a rapid responder. The average CAI significantly decreased from 11.7 to 4.2 (P < 0.01). Seventy-four percent of the patients responded to the therapy, and 53% of these patients were rapid responders. The following significant factors correlated with the rapid LCAP response: (i) steroid resistance (P < 0.05), (ii) severe disease indicated by a CAI score greater than 11 (P = 0.05), (iii) disease duration of less than 1 year (P < 0.05), and (iv) C-reactive protein levels before treatment (P < 0.01). These results suggest that the early initiation of LCAP is beneficial in patients with steroid-resistant UC.