Glycoprotein I(β 2GPI) has been identified as a cofactor in the recognition of phospholipid Ag cardiolipin (CL) by anticardiolipin Ab(aCL) purified from patients’ serum with autoimmune disease. However, there is a considerable controversy as to the antiβ 2GPI antibodies occurred in aCL. In order to select β 2GPI recognizing molecules, β 2GPI was used as a probe to screen affinity phage clones panned from a phage peptide library. After four cycles of selection, the phage recovery increased from 2.4×10 -5 % to 1.1×10 -3 %, indicating that a specific enrichment had been achieved. In order to characterize these phage clones, we investigated their specific binding to β 2GPI and their inhibition of β 2GPI binding to antiβ 2GPI antibodies. Almost 40 percent of clones reflected considerable binding abilities and inhibitory activities towards antiβ 2GPI antibodies. A group of related peptides were identified by DNA sequencing, in which there were seven related peptide sequences, with four of them representing more than once. These peptide sequences display similarities at several positions. Sequence motif (—F—S—L—) was evident in most of the peptides. It suggests that these peptides may specifically block the antiβ 2GPI antibodies binding to β 2GPI. Our result supports the idea that β 2GPI acts as a Ag for these antiβ 2GPI antibodies occurred in the aCL. Glycoprotein I (β 2GPI) has been identified as a cofactor in the recognition of phospholipid Ag cardiolipin (CL) by anticardiolipin Ab (aCL) purified from patients’ serum with autoimmune disease. However, there is a considerable controversy as to the antiβ 2GPI antibodies occurred in aCL. In order to select β 2GPI recognizing molecules, β 2GPI was used as a probe to screen affinity phage clones panned from a phage peptide library. After four cycles of selection, the phage recovery increased from 2.4 × 10 -5% to 1.1 × 10 -3%, indicating that a specific enrichment had been achieved. In order to characterize these phage clones, we investigated their specific binding to β 2GPI and their inhibition of β 2GPI binding to antiβ 2GPI antibodies. considerable binding abilities and inhibitory activities towards antiβ 2GPI antibodies. A group of related peptides were identified by DNA sequencing, which there were seven related peptid It means that these peptides may specifically block the anti beta (-F-S-L-) was evident in most of the peptides. 2GPI antibodies binding to β 2GPI. Our result supports the idea that β 2GPI acts as a Ag for these antiββGPIs occurred in the aCL.