The present study examined the effects of carbon monoxide (CO) intoxication and aging on learning and memory deficit in young($5{sim}8$ weeks) and aged($52{sim}66$ weeks) mice, using the step down and step through passive avoidance failure techniques. We also investigated the effects of ginseng saponins on memory deficit. Significant decrease in memory registration, retention and retrieval function in young mice and decrease in memory registration and retention function in aged mice were observed. Normal young mice were apt to perform to a great degree of passive avoidance response than normal aged mice, but there was no difference between both groups by CO exposure. Administration of ginseng saponins showed an improvement on passive avoidance failure induced by CO exposure.