The Goal of this study was to assess the effect of aerobic exercise on cognitive function of elderly people. The participants' cognitive functions were measured before exercise. Exercise was practiced three times a week for nine weeks. The aerobic exercises consisted of warm-up exercises for five minutes followed by cycling for 30 minutes. The exercise intensity was set to 65%~75% of the intensity for the maximum heart rate(220-age). The control group did not perform any exercises. The subjects' cognitive functions were measured nine weeks later. In the aerobic exercise group, between before and after the exercises, significant increases appeared in total K-MMSE scores and scores of some sub items comprising memory registration, concentration and calculation abilities but not in other items. In the control group, no significant differences appeared in any items between before and after the experiment. In a comparison between the aerobic exercise group and the control group, significant differences appeared in total K-MMSE scores and scores of two sub items comprising concentration and calculation abilities but not in other items(p<.05). Aerobic exercises were effective in the improvement of cognitive functions and among sub items of cognitive functions, concentration and calculating abilities were improved. Aerobic exercises performed by elderly persons are considered to be effective in improving cognitive functions.