Macrophage activation syndrome (MAS) and widespread brain lesions are rare and severe complications of childhood-onset systemic lupus erythematosus (SLE). We report an 11-year-old girl who presented with recurrent rashes for half a year and fever for 2 weeks. Clinical and laboratory features at admission pointed to the diagnosis of SLE and SLE-associated MAS. Cerebral magnetic resonance imaging taken on day 4 after admission showed abnormal signals. Glucocorticoid therapy was started on day 5. Two days later, the patient appeared weak and ill, then the next day she exhibited dizziness, drowsiness, apathia, and dysarthria. High-dose methylprednisolone, cyclophosphamide, and intravenous immunoglobulin were used to treat the patient, and intrathecal dexamethasone was given. The patient was discharged on day 30 after admission and showed complete clinical resolution and improved magnetic resonance imaging resolution.