Electrolytic capacitors used for smoothing DC link voltage is one of the major root causes of fault in power electronic system. The aging of aluminum electrolytic capacitors is expressed by the increase of their equivalent series resistance (ESR) and the reduction of their capacitance. Thus, the proposed technique in this paper is to measure capacitance, by comparing energy loss of DC link capacitors with stator resistor in electric machine. Condition of DC link capacitors can be estimated from the capacitance decrease rate between initial and aged capacitors. The results show that the proposed technique provides an easy, widely applicable and simple low cost solution for detecting dc link capacitor degradation.