We describe our surgical experience of inflammatory abdominal aortic aneurysm (IAAA) in a 54-year-old man. Computed tomography (CT) with contrast enhancement revealed an infrarenal abdominal aortic aneurysm with marked thickening of the aneurysmal wall (mantle core sign) and left hydronephrosis. The left ureteral stenting was performed. Preoperative laboratory findings showed high levels of serum IgG4. The IAAA was removed and replaced with a woven-Dacron graft in situ. Histological examination revealed the IgG4 positive plasma cell, and demonstrated IAAA associated with IgG4. The postoperative serum IgG4 was reduced, but remained high. The postoperative CT revealed new right hydronephrosis, and the ureteral stent was performed. The mantle sign reduced in CT scan after steroid therapy. IAAA with hydronephrosis seems to be associated with IgG4-related sclerosing disease. In this case, the levels of serum IgG4 seems to be a good index for treatment efficacy.