We present two cases of systemic lupus erythematosus (SLE) associated with both Basedow's disease and fatty liver. The first case is a 46-year-old Japanese female who was admitted because of high fever and general fatigue. She had been diagnosed as having Basedow's disease and treated with thiamazole for over 4 years. Since thiamazole-induced lupus was unlikely because of high titer anti-nuclear antibody and anti-DNA antibody and low levels of complements, a diagnosis of SLE was made. The upper abdominal ultrasound study and the specimen obtained by liver biopsy performed before initiating steroid therapy demonstrated marked fatty liver. SLE itself is considered as an etiology of fatty liver in this case. The second case was a 25-year-old Japanese female with SLE. She had been treated with prednisolone for 13 years and was complicated with Basedow's disease 10 years later. Fatty liver was also demonstrated in this patient on ultrasonography, and was thought to be resulted from long-term steroid hormone administration.