Oxidized low-density lipoprotein (Ox-LDL) plays an important role in the initiation and progression of atherosclerosis. Asp-hemolysin, a hemolytic toxin from Aspergillus fumigatus, is a specific, high affinity binding protein for Ox-LDL. We have previously shown that Ox-LDL strongly inhibits the hemolytic activity of Asp-hemolysin, and that the removal of lysophosphatidylcholine (lysoPC) from Ox-LDL abolished the inhibition. In the present study, to clarify the binding mechanism of Asp-hemolysin to Ox-LDL, we investigated the interaction between Asp-hemolysin and lysoPC as a typical lipid moiety of Ox-LDL. Based on western blot analysis, the binding of Asp-hemolysin to LDL, oxidized for different times, depended on the lysoPC content in each Ox-LDL. In addition, the inhibition of lysoPC production in Ox-LDL by phenylmethylsulfonyl fluoride (PMSF) pretreatment of LDL resulted in a marked decrease of Asp-hemolysin binding to PMSF-pretreated Ox-LDL. Furthermore, the binding analysis of Asp-hemolysin to lysoPC using ion-exchange chromatography revealed that Asp-hemolysin directly binds to lysoPC.