A 77-year-old woman with knee osteoarthritis (OA) complained of right (ipsilateral) knee pain for more than 5 years with gait asymmetry. The OA and quadriceps muscle weakness were more severe in the left (contralateral) knee, but she had no pain. Bracing of the left knee led to decreased gait asymmetry, as determined with an inertial measurement unit, and reduced pain in the right knee.This case highlights the contralateral knee effect on ipsilateral chronic knee pain, possibly through gait asymmetry. These findings provide a mechanistic insight into knee OA-related pain in patients with gait asymmetry and suggest a new rehabilitative approach.