Inflammatory pseudotumor (IPT) of the liver is rare, and differential diagnosis from malignant tumors is difficult. We herein report a case of IPT of the liver with marked elevation of carbohydrate antigen 19-9 (CA19-9). A 72-year-old woman, who underwent low anterior resection for rectal cancer, had low-grade fever and epigastric pain. The patient has well-controlled idiopathic thrombocytopenic purpura (ITP) with steroid maintenance treatment. Abnormal laboratory findings included serum carcinoembryonic antigen of 15.9 ng/mL and CA19-9 up to 14,632 U/mL. Computed tomography revealed a low-density lesion, and magnetic resonance imaging demonstrated a high intensity lesion on T1, T2-weighted, and diffusion-weighted images (55 × 22 mm in the Couinaud's segment 4 of the liver). However, 1 month after the appearance of the symptom, serum level of CA19-9 suddenly decreased to 37 U/mL. The tumor decreased spontaneously to 20 × 10 mm. Seven months later, the tumor had reduced to 18 × 11 mm. With a diagnosis of IPT, the patient remains well without regrowth of the tumor at 1 year follow-up after CA19-9 decrease to normal limits.