Abstract: Effects of light stress on function and structure characteristics of photosynthetic membranes (thylakoid membranes and PS Ⅱ particles) in leaves of wheat( Triticum aestivum L.cv.Yangmai No.5)seedling were studied by measuring changes in O 2 evolving activity,fluorescence emission spectra and membrane protein polypeptide components. Results showed that light stress (2 500 μmol·m ^-2 ·s ^-1 ) induced decline of electron transport activities of thylakoid membranes and PS Ⅱ particles and decrease in fluorescence emission intensities. When PS Ⅱ particles in wheat leaves were illuminated with higher light intensity (2 500 μmol· m ^-2 ·s ^-1 ) at 25 ℃, the extrinsic protein (OEC 33 000,23 000,17 000 u) and the chlorophyll binding protein CP43 of PS Ⅱ complex were degraded. It seems that OEC 33 000 u polypeptide plays a role in regulating stabilization of the PS Ⅱ reaction center structure under light stress.