Aim To develop a sandwich ELISA for measuring serum β2-glycoprotein I-lipoprotein (a) complex ((β2-GPI-Lp(a)) concentration,and to explore the existence of serum complexes β2-GPI-Lp(a) and its clinical value for IgA nephropathy. Methods ELISA was established using rabbit anti-human β2-GPI antibody as the capture antibody,and quantitating with polyclonal antibody against apolipoprotein (a) enzyme conjugate. The concentrations of β2-GPI-Lp (a) complexes were studied in 50 patients with IgA nephropathy and 50 control subjects. Results Mean intra-assay and inter-assay coefficients of variation of the assay were 6.61% and 13.02%,respectively. Linear range of the assay was between 0.33~1.83 ku/L. Serum β2-GPI-Lp(a) concentrations in IgA nephropathy were significantly higher than those of controls (1.45±0.57 ku/L vs 0.42±0.29 ku/L,P<0.01). Forty patients (80%) were found to have elevated β2-GPI-Lp(a) concentrations,whereas only two out of the fifty healthy controls had high β2-GPI-Lp(a) levels. Conclusions β2-GPI may form complexes with lipoprotein (a) in circulation. β2-GPI-Lp(a) complexes concentration was increased in patients with IgA nephropathy,suggesting its potential clinical value as a diagnostic marker for IgA nephropathy.