The methods such as vibration monitoring and temperature monitoring are usually adopted in the predictive maintenance of the rotational machinery. However, these methods have limitation, especially for in-service monitoring of motors, as their predictive time of the accidents is short and defective. Detection of metallic particle in engine oil can indirectly predict wear status of its bearings and gear etc., which is important to prevent engine failure caused by over wear. In this paper, an eddy current testing (ECT) method for inspection of metallic particles in engine oils, the design of the ECT system consisting of sensor, hardware and software, and the realization of the on-line monitoring are described. In addition, the prospect for the on-line “cloud” monitoring of engine oil abrasive particle is also discussed.