The health services system in Thailand has been changing rapidly. Particularly in the social security scheme, quality and efficiency have been strongly emphasized since its establishment in 1991 as the scheme applies capitation payment to fund providers-so called main contractors-prospectively. Although the payment mechanism is beneficial to the overall system administration and helps contain operating costs of the Social Security Office, the capitation payment makes contracted hospitals at risk of financial burden of medical care offered to social security patients. The risk might affect clinical practices and quality of services contracted hospitals providing to the beneficiaries. The Social Security Office should, therefore, has an quality indicator system to monitor contracted hospitals for quality assurance, to promote of quality improvement among the hospitals and to inform beneficiaries when they make their choices of contracted providers