Purpose : The main purpose of this study was to investigate the influence of lower extremity strengthening on balance ability of knee osteoarthritis. Methods : The walking exercise group with modality treatment and strengthening exercise group with modality treatment. The walking exercise and strengthening for 40 minutes per day and three times a week during 6 weeks period. Short Form McGill Pain Questionnaire(SFMPQ) was used to measure patient's pain level. Patient Specific Functional Scale(PSFS) was used to measure patient's functional disability level. BPM was used to measure sway area. Global Perceived Effect Scale(GPES) was used to measure recovery or worse of patient's condition. Results : 1. SFMPQ was strengthening exercise group showed significantly decreased more than walking exercise group(p