Photosynthesis in iron-deficient soybean and maize leaves decreased drastically. The quantum yield of photo system 2(PS2) electron transport (φPS2), the efficiency of excitation energy capture by open PS2 reaction centres (Fv'/Fm'), and photochemical quenching coefficient (qp) under high irradiance were lowered significantly by iron deficiency, but non photo chemical quenching (NPQ) increased markedly. The analysis of the polyphasic rise of fluorescence transient showed that iron depletion induced a pronounced K step both in soybean and maize leaves. The maximal quantum yield of PS2 photochemistry (φpo) decreased only slightly, however, the efficiency with which a trapped exciton can move an electron into the electron transport chain further than QA (ψO) and the quantum yield of electron transport beyond QA (φEO,) in iron deficient leaves decreased more significantly compared with that in control. Thus not only the donor side but also the acceptor of PS2 was probably damaged in iron deficient soybean and maize leaves.