Development of two-wire body weight support (BWS) system for interactive treadmill (ITM). This BWS system was developed having compact size to install in clinics without major space alterations. The ITM can naturally adjust the walking speed according to user’s intention for changing walking speed. Thus walking training on ITM can provide similar walking with overground walking. Recently, conjunction of treadmill and BWS system are being frequently used in clinical practice because of space effectiveness and safety. In order to provide effective and safe gait training using an ITM, a BWS system suitable for an interactive treadmill has been developed. This paper presents the BWS system and harness design and experimental validation, including the system model and force. According to experimental result our two-wire BWS system can provide adequate BWS until 0.6m/s with 300N.