Abstract: After exposing etiolated wheat seedlings to intermittent light (cycle of 2 min. light, 118 min. dark) for 24 hr., we obtained an incompletely developed chloroplast membrane. It was then compared with a completely developed chloroplast membrane obtaining from wheat seedlings grown under normal light-dark regime. We investgated the effect of various cations and their concentrations on the absorption spectrum and the photosystem Ⅱ function of the above two types of chloroplast membranes. A similar effect of potassium and magnesium ions on the absorption spectra of completely developed chloroplast membrane was observed. They decreased the absorption peak values at both the red and blue regions of the chloroplast membrane in the same manner. The degree of decrease in the peak value is proportional to ion concentration. But in the incompletely developed chloroplast membranes similar phenomenon was not observed. In the presence of K+ and Mg2+ of various concentrations, the absorptionn peaks at the red region overlapped almost completely, and these at the blue region only changed slightly with ion concentrations. DCIP photoreduction rate of the two types of chloroplast membranes was stimulated by the addition of K+ and Mg2+ in various concentrations. But the degree of stimulation in the two types of membranes was quite different. In the presence of l00 mM KCl or 5.0 mM MgCl2, DCIP photoreduction rate of completely developed chloroplast membranes was enhanced by 76.8% and 68.9% respectively, whereas in incompletely developed chloroplast membranes it was only increased by 56.3% and 36.4% respectively. The causes of the effects of cations on the absorption spectrum and the photosystem Ⅱ function of two types of chloroplast membranes were discussed.