Abstract: Objective: To investigate the prevalence, their autoantigen and the clinical significants of antiendothelial cell antibodies (AECAs) in systemic vasculitis. Method: Western blotting was performed to detect specific AECA in sera of systemic vasculitis, SLE, RA, SS and healthy donors. Then analyse the relationships of AECA with the disease manifestation. Result: (1) The prevalence of AECA was 77.7% in systemic vasculitis, 87.5% in SLE, 66.7% in SS, 7.14% in RA, and 10% in normal group, respectively. (2) AECA reacted with a heterogenerous series of endothelial proteins which ranged in molecular size feom 16 to 120kD. Furthermore, AECA against a 47kD endothelial cell antigen were more frequently found in a variety of systemic vasculitis and SLE. (3) Compared with those in AECA-negative patients, the mean levels of ESR in AECA-positive patients with TA and the mean levels of BVAS in patients with WG, MPA and CSS were both significantly higher in AECA-positive patients. Patients with BD who have AECA aganist 47kD endothelial cell proteins were more frequently found to have neuropathy than those 47kD-AECA-negative patients, and the prevalence of inhanced CRP are also more frequent. Conclusion: AECA showed to be correlated with the disease manifestation, and the same molecular size antigen could be found in a variety of systemic vasculitis and SLE.