Synchrotron radiation X‐ray diffraction has been intensively applied to bacteriorhodopsin photointermediates to understand the molecular mechanism of light‐driven proton pump. Time‐resolved X‐ray diffraction with time resolution of 244msec revealed that the two types of the structures appear during a photocycle. In order to realize the time resolution of 5&mgr;sec, we developed a new snap shot diffraction technique. With the method, we revealed that the structural change is triggered by the deprotonation of Schiff base. Based on the structures, we proposed a conformation‐controlled conformational change model. The apparent discrepancy between crystal structures and low resolution structures is also discussed. © 2004 American Institute of Physics