Inefficiency of urban rail transit systems (URTS) results in a lower standard of service than required and has negative economic impacts. Many efforts have been undertaken to calculate the efficiency of URTS or their subunits. Overall equipment efficiency (OEE) as a measure of efficiency is a simple, flexible, and efficient formula. The OEE measure ensures that equipment is available and fully capable of producing quality goods/services for the maximum time of operation and is being used in a proper way. This paper discusses the idea of the OEE from the field of production and how it can be applied to a URTS. Overall efficiency of rolling stock (RS) is a major influencing factor on the efficiency of URTS. Therefore, the three fundamental parameters of OEE—availability, performance, and service quality—are defined for the RS of a URTS, and a method for their calculation is presented. The usefulness of OEE for URTS is investigated.