Systemic lupus erythematosus (SLE) concomitant with thrombotic thrombocytopenic purpura (TTP) in children is rarely diagnosed. We report a case of a 15-year-old girl with butterfly patch, generalized edema, leg pain, anemia (Hb 74 g/l), thrombocytopenia (5 x 109/l), schistocytes in peripheral blood smear, acute kidney injury (eGFR 27 ml/min/1.73 m2), proteinuria, and erythrocyturia. The direct Coombs test was positive, and warm antibodies (IgG) were detected on red blood cells. ANA in titer 1 : 2560, low serum C3 and C4 complement level, ADAMTS13 (a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13) activity < 4% and the presence of ADAMTS13 inhibitor were detected. In renal biopsy class IVA/V lupus nephritis was diagnosed. Her clinical symptoms fulfilled criteria for the diagnosis of SLE and the diagnosis of TTP. She was treated with intravenous methylprednisolone and cyclophosphamide 750 mg/1.73 m2/monthly for six months, followed by oral prednisone with azathioprine, chloroquine, and enalapril. The long-term clinical outcome was good. We report a case rare in adolescents, TTP related to SLE, which may suggest the need to test for ADAMTS13 activity and the presence of ADAMTS13 inhibitor in children with SLE and anemia, thrombocytopenia and rapid deterioration of renal function, to make the right therapeutic decisions.