The mechanism of radiation induced electron transfer within a series of binary molecular aggregates, which were composed of myosin and caffeic acid with varied molar ratios (r) of amino acid residues in myosin to caffeic acid, has been studied by resolution of composite ESR spectra recorded at 77 K. A series of spin transfer ratios (R,ST,) defined as the spin concentration ratios of caffeic acid anion radical arising from transfer of captured electron by peptide chain of myosin to that from directly trapping of secondary electrons by caffeic acid were obtained . A series of R,ST, were plotted against r varied from 1:1 to 100:1. A linear relationship between Rs,T, and r demonstrates that Rs,T, increase linearly with decrease of caffeic acid content. The capture of radiation induced secondary electrons depend on the electron affinities of components including electron affinitive amino acid residues and peptide carbonyl of myosin and caffeic acid. The process of electron transfer along peptide chain and trapping on caffeic acid finally has been elucidated based on the comparison of the energies of lowest empty molecular orbital(E,LUMO,) of the electron affinitive components and reaction rate constants of ,http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=42650684&type=,http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=42650702&type=,http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=42650685&type=, with these components respectively using pulse radiolysis techniques.