We present a 60-year-old female patient with asymptomatic acute hepatitis E that was fortuitously detected during the course of ulcerative colitis (UC). She was admitted to hospital on October 30, 2015. Endoscopy and histological examination of the colon showed typical findings of UC. All parameters of liver function tests were normal on this date. Combination therapy with oral prednisolone and mesalazine was started and intravenous administration of infliximab once every 8 weeks was added later. Her symptoms gradually improved after these treatments, and she was discharged on February 7, 2016. In a periodic check-up on July 7, 2016, high levels of serum transaminases were detected in liver function tests. Although drug-induced liver injury was first suspected, anti-hepatitis E virus (HEV) immunoglobulin A was positive. The genotype and subgenotype of this HEV are 3 and 3a, respectively, although the infectious route of the HEV was unclear. Within 2 weeks after the onset of acute liver injury, the HEV viremia disappeared and her liver function tests improved. Examination of serum anti-HEV immunoglobulin A should be added at the time of abnormal liver function tests in patients with UC receiving immunosuppressive and biological drugs.