Objective To investigate the clinical significance of anti-β2 glycoprotein Ⅰ(anti-β2GP Ⅰ)antibodies in patients with systemic lupus erythematosus(SLE)and to assess their association with lupus thrombocytopenia.Methods Anti-β2GP Ⅰ antibodies were tested in 108 SLE patients(including 37thrombocytopenia patients),30 patients with rheumatoid arthritis(RA)and 30 healthy individuals by enzyme-linked immunosorbent assay(ELISA).The clinical features and laboratory findings were collected,and the associations of anti-β2GP Ⅰ antibody with laboratory findings and disease activity were analyzed.Results Sensitivities of anti-β2GP Ⅰ antibody were 19.44%(21/108)in SLE and 10%(3/30)in RA,respectively.The specificity of anti-β2GP Ⅰ antibody was 95.0% in SLE.The anti-β2GP Ⅰ antibody titers of the SLE group were significantly higher than normal group(P ＜ 0.05).There was no significant correlation between anti-β2GP Ⅰ antibodies and thrombocytopenia(r =-0.028,P ＞0.05).Anti-β2GP Ⅰ antibody was positively correlated to anticardiolipin antibody(r = 0.566,P ＜ 0.01).No associations were found between anti-β2GP Ⅰ antibody and other clinical and laboratory features.There was no statistical correlation between the level of anti-β2GP Ⅰ antibody and SLEDAI scores.Conclusions Anti-β2GP Ⅰ antibody had high specificity in SLE.There was no significant correlation between anti-β2GP Ⅰ antibodies and lupus thrombocytopenia.