Autoimmune pancreatitis (AIP) is treatable with steroids, but relapse is frequent. The efficacy of steroid pulse therapy has been shown for various autoimmune diseases, but has not become established therapy. In this study, we reviewed the efficacy of steroid pulse therapy in 24 subjects who were diagnosed with AIP type 1 at our hospital. Patient characteristics, time-course of serum IgG4, and the cumulative relapse-free survival rate were compared between patients who received oral steroid therapy (oral group) and those who were treated with steroid pulse therapy (pulse group). Serum IgG4 was reduced significantly after therapy in both groups and the 5-year cumulative relapse-free survival rates in the two groups did not differ significantly (oral group 46.9%, pulse group 77.8%). However, in a subset of cases with diffuse pancreatic swelling, this rate was significantly lower in the oral group (33.3% vs. 100.0%, p = 0.046). These results suggest that steroid pulse therapy is effective for prevention of relapse in AIP patients with diffuse pancreatic swelling.