We herein report a case of ulcerative colitis (UC) exacerbated by strongyloidiasis. Parasites including Strongyloides stercoralis and Entamoeba histolytica can cause chronic gastrointestinal inflammation and long-lasting symptoms resembling UC. On the other hand, it is not well-known that such organisms can trigger the exacerbation of pre-existing UC. We would like to highlight the importance of recognition of strongyloidiasis in the management of UC patients who have lived in or migrated from endemic regions, such as Asia, Africa, and South America.