This study aimed to replace the current discontinuous rail monitoring system by applying “Plug and Play” technology to axle bearing monitoring system of railroad vehicle to enable real-time monitoring, and by confirming on-condition maintenance efficiency and reliability. It researched a wireless sensor monitoring system which uses SAW (Surface Acoustic Wave) sensor technology to monitor temperature changes in the axle bearing during operation. The temperaure change was monitored by pilot SAW sensor which KRRI designed and developed this sensor for the high speed railroad vehicle. The results of the experiment were compared with HDB measurements to confirm the reliability of the real-time monitoring results measured on vehicles during operation