Falls cause to fracture, brain damage, and musculoskeletal disease as secondary injury. Persons who experienced fall are afraid of other falls and decreased in physical - social activity. Risk factors of falls are various and one of them is muscle weakness of lower extremity with aging. The purpose of this study is to examine improvement of balance after strengthening exercise on ankle joint which muscle weakness is conspicuous and to prevent elderly persons from falling. The subjects were composed of 15 normal elderly persons over 55 years, classified by experiment group(9) and control group(6). This study was executed from March 5, 2001 to April 20, 2001. Experiment group performed 5 ankle muscle strengthening exercises three times per week. To evaluate strength and balance improvement, muscle strength of subject was measured by Cybex 6000 and balance was evaluated by one - legged stance test and agility, dynamic balance test. The data was analyzed by covariance with pretest value to determine whether differences between the groups because pre-test values were significant difference between the groups. As it was analysed by covariance with pre - test value, the ankle plantar flexor sowers with knee flexion were significant difference between groups(p=.006) and the ankle dorsi - flexor powers with knee were significant difference between groups(p=.040). The ankle plantar flexor powers with knee extension were not significant difference between groups(p=.112) and the ankle dorsi - flexor powers with knee extension were not significant difference between groups(p=.360). The one - legged stance times were not significant difference between groups(p=.643) and the agility, dynamic balance times were significant difference between groups(p=.001). In the plantar, dorsi - flexor power with knee flexion and agility, dynamic balance time were significant difference between groups. But in the plantar, dorsi - flexor power with knee extension and one-legged stance time were not significant difference between groups. In the plantar, dorsi - flexor power with knee flexion and the agility, dynamic balance time were increased, so strengthening exercises of ankle joint were effective on muscle force and balance improvement. The correlation coefficience between plantar flexor power with knee flexion and one - legged stance time was increased from .27 to .62. It means that increasing of muscle force influenced in balance improvement.