Abstract: The light discrimination and retention in maze and in avoidance box were seriously impaired after bilateral large area electrolytic lesions of the hippocampus in rats.The impairment involved not only the responses learned before operation but also the relearning ability.No effect was found in those animals with lesion of equal amount of area in cortical area.The results of local electrotytic lesion on dorsal or ventral hippocampus showed that the ventral part of hippocampus played an important role in light discrimination retention in maze while the dorsal part of hippocampus was not essential to these responses.