Wireless sensor networks with on-board signal processing capabilities are becoming very attractive for machinery condition monitoring purposes. Their advantages in cost and size are becoming an important factor for deployment in a new generation of maintenance-e-maintenance. In this paper, an intelligent monitoring system for emaintenance (IMSEM) is presented using a recently developed and tested MEMS accelerometer, a low-power microprocessor and a wireless communication module. The system has a compatible framework and interface with Open Systems Architecture for Condition-Based Maintenance (OSA-CBM). Importantly, it integrates OSA-CBMdefined functions, including sensing module, signal processing, condition monitoring and health assessment; thus, the developed system can successfully reduce-the monitoring complexity and communication overhead with human operators. The performance of IMSEM is evaluated by carrying out fault diagnostic on rotating unbalance of a mechanical shaft driven by a DC motor with varying loads and speeds. By analysing the signals from the vibration signal and rotating speed, the IMSEM has the ability to carry out on-board fault detection and diagnosis. The IMSEM achieved an accuracy of 95% in detecting the fault and severity of rotor unbalance, which is based on the ISO 1940-1:2003.