We describe a previously healthy 9-year-old girl who had multiple purpura several days after acute adenovirus gastroenteritis and mycoplasma pneumonia. Initial laboratory evaluation revealed a prolonged prothrombin time (PT) and APTT, low complement levels (C4, CH50), and positive immune complex (C1q) in her serum. Platelet count, fibrinogen, and other routine blood chemistry tests were normal. The prolonged APTT was not corrected by mixture of the patient's plus normal plasma. Clotting activities of factors II, V, VIII, IX, X, XI, and XII reduced. Further examinations revealed the presence of lupus anticoagulant (LA), phosphatidylserine-dependent anti-prothrombin antibodies (aPS/PT), and anticardiolipin antibodies. Mycoplasma pneumonia was treated by minocycline and the patient's skin lesions disappeared spontaneously within a week. During follow-up, she showed no other bleeding symptoms, and no signs of SLE or other autoimmune diseases. Four weeks after admission to our hospital, blood coagulation tests and serum complements normalized. Clotting activities of factors and antiphospholipid antibodies were not detected, half year later. The bleeding in this case was associated with acquired hypoprothrombinemia caused by antiphospholipid antibodies following acute adenovirus gastroenteritis and mycoplasma pneumonia.