Objective To investigate the clinical significance of D-dimer in systemic lupus erythematosus (SLE). Methods The study group comprised 261 SLE patients who were admitted in ward from 2005 to 2008 in Peking University People's Hospital Collect the clinical data to investigate the clinical significance of D-dimer. Results ( 1 ) The D-dimer levels of 56 patients were increased due to coexist reduced renal function, infections, disseminated intravascular coagulation ( DIC), liver disorders, pregnancy and injury. With the exception of above patients, 142 ( 69. 3 ) patients were increased in total 205 patients. (2)The level of D-dimer was positively correlated with SLE disease activity index( SLEDAI ) score ( r =0. 598,P =0. 000), and was associated with anti-dsDNA antibody, ESR, C-reactive protein(CRP) and complement C3 and C4. (3)D-dimer level was associated with important organ involvement. (4)All patients with thrombosis had increased D-dimer, but patients without thrombosis had normal or increased D-dimer levels. Conclusion The level of D-dimer elevates in patients with active disease or important organ involvement , it can not identify thrombosis. All patients with thrombosis had increased D-dimer levels.