The role of lvsine residues in the structure and function of bacteriorhodopsin(bR) was studied by the chemical modification method──acetylation. After acetylation, the photoresponse signals and the decay of photocycle intermediate M412 were slowed down while the yields of M412 were decreased. But UV/VIS absorption spectra did not show that the conformation around retinal chromophore was disturbed by acetylation. The effect of acetylation was weakened by high pH or salt media. The results imply that lysine residues do not directly participate in the proton translocation. instead, they affect this process by their contribution to the surface protentials.