We report a case in which daibofuto was effective for knee osteoarthritis in the elderly. The case was an 84-year-old woman, who tried various drugs for right knee pain at multiple hospitals, but the effect was insufficient, so she visited the hospital hoping for Kampo treatment. Although no qi deficiency was observed systemically, joint swelling and mild heat sensation were observed locally. Additionally, in plain X-ray findings, severe knee osteoarthritis including joint space narrowing, osteophyte formation, and osteosclerosis was observed. We administered sokeikakketsuto and hachimigan, but no effect was obtained. Since daibofuto was effective to some extent, we changed to a decoction and increased the amount of crude drug, and then sufficient effect was obtained. Daibofuto has an effect on qi deficiency, and it is frequently used for rheumatoid arthritis with mild synovitis. Daibofuto was also effective for knee osteoarthritis in the elderly ; therefore we believe that both diseases have a common pathological condition.