We report an erythema nodosum (EN) patient whose condition became apparent during the clinical course of ulcerative colitis (UC). The patient relapsed frequently in spite of taking a high dose adrenocortical steroid during his morbidity period of UC. Monocyte-granulocytapheresis (M-GCAP) was combined with 5-aminosalicylic acid 2250 mg/day peroral and once a day of steroid enema. Monocyte-granulocytapheresis was performed once a week for 5 weeks, and succeeded in inducing clinical remission for both UC and EN. The immunological and clinical connections between UC and EN have never been fully elucidated. In this case, because the symptoms of UC and EN revealed parallel improvement after his inflammatory reaction had been brought under control by combining M-GCAP therapy, we hypothesize that the onset of EN appeared as a result of the patient's long-term, treatment-resistant immuno-disturbance, which first appeared as symptoms of UC. Immunomodulative effects induced by M-GCAP might help to control other chronic non-specific inflammations not concerned with targeted organ(s).