Abstract: In this paper,we have evidenced that ChllA dimer sample is (Chla-H₂O)₂ by direct measurements of the whole soybean (or spinach) leaf ESR. For chlorophyll ESR measurements, the leaves were irradiated with ultraviolet lamp and continuous He-Ne laser. The signal of (Chla-H₂O)₂⁺. and signal I of the whole soybean leaf have same origin. Therefore (Chla-H₂O)₂ can simulate that the investigations of the organization and function of the soybean leaf reactioncenterOur experimental date show that the soybean leaf ESR spectrum can beanalysed by the radical Pair theory.