Quality has become important issues for every health care service organizations. Most hospitals have strived to achieve quality excellence in order to gain competitive advantage through different strategies. By understanding the current level of efficiency of each hospital, it could determine suitable quality mechanism and provide right amount of resources. The objective of this paper is to demonstrate how to assess the operating efficiency of the hospitals which adopted hospital accreditation (HA) and international standard (ISO) by using Data Envelopment Analysis (DEA) method. Data was collected from hospitals under Medical Service Department, Bangkok, Thailand. The results show that four hospitals are efficiently operated. Overall, the average efficiency score of the hospitals are quite high. The average efficiency score for hospitals with hospital accreditation and with ISO equal to 0.9022, 0.8802, respectively. Finally, this DEA approach provides top management a framework to evaluate the operating efficiency of hospitals and insights for appropriate resource allocation.