Background: Almost all surgeries for ulcerative colitis (UC) are performed under immunosuppressive conditions. Immunomodulators or biologics, with the exception of corticosteroids, do not appear to be risk factors for post-operative infectious complications. However, many patients are on multiagent immunosuppressive therapy at the time of surgery. Therefore, we evaluated the influence of pre-operative multiple immunosuppressives on the occurrence of surgical site infection (SSI) in UC. Methods: We reviewed surveillance data from 181 patients who underwent restorative proctocolectomy between January 2012 and March 2014. The incidences of SSI and the possible risk factors among patients receiving different immunosuppressive therapies were compared and analyzed. Results: The incidence of incisional (INC) SSI was 13.3% and that of organ/space (O/S) SSI was 7.2%. The number of immunosuppressives did not significantly correlate with each incidence. Total prednisolone administration ≥12,000 mg (OR 2.6) and an American Society of Anesthesiologists score ≥3 (OR 2.8) were shown to be independent risk factors for overall SSI, whereas corticosteroid use in INC SSI (OR 17.4) and severe disease (OR 5.2) and a large amount of blood loss (OR 3.9) in O/S SSI were identified as risk factors. Conclusion: Although a correlation between multiple immunosuppressive therapy and SSIs was not found, it is not recommended that all patients be treated with multiple immunosuppressive therapy. Treatment strategy should be applied based on the patient's condition.