Abstract: (1) Similar results were obtained after controlled digestion of spinach chloroplasts with trypsin and chymotrypsin, but the specificity of digestion of chymotrypsin differed from that of trypsin. Trypsin weakly uncoupled photosynthetic electron transport but chymotrypsin did not. (2) Both changes of DCIP and Fecy reduction activity and the recovery of CCCP inhibition by electron donors of PSⅡ during proteolytic enzyme digestion showed that trypsin not only affected oxidizing side and reducing side of PSⅡ, but also partially inactivated the reaction center of PSⅡ. (3) The effects of CCCP on photosynthetic electron transport in chloroplasts digested with trypsin and chymotrypsin indicated the probable presence of "channel" in PSⅡ. These results support the interpretation that there is a fine structure in PSⅡ membrane. Modification of the protein components of PSⅡ in the membrane might alter their function.