This paper presents an application of wireless sensor networks (WSN) to an in-service motor monitoring and energy management system. Based on the IEEE 802.15.4 standard, wireless sensor devices are developed in the proposed system. The motor current and voltage signals are acquired and analyzed by a DSP device to get the condition of motors, and the results are transmitted over the wireless network to a central supervisory station (CSS), where they are stored, displayed and analyzed to meet the requirement of motor monitoring and energy management. This approach greatly reduces the transmission time. That makes the proposed system acceptable in real-time cases. The wireless sensor devices are demonstrated and the test results are given.