OBJECTIVES: To further examine preferred drug benefit plan for civil servant medical benefit scheme (CSMBS) in Thailand. METHODS:  Two types of questionnaires modified from previous studies were sent to 1,000 conveniently selected civil servants residing in two provinces. The questionnaire included ten hypothetical drug benefit plans containing four attributes e.g. cost sharing, formulary, accessibility, and quantity.  Those two questionnaires contained different types of the cost sharing attribute, copayment and coinsurance. The respondents were asked to rate their satisfaction levels of each plan on Likert scale.  Conjoint analysis was used to calculate utility weights and relative importance. RESULTS:  Results from 293 questionnaires having copayment, as the cost sharing attribute, showed the beneficiaries weighed highest importance, 30.18%, on the formulary attribute. The beneficiaries preferred having access to drugs both listed and not listed in national essential drug list.  The second important attribute was the cost sharing and its relative importance was 24.97%. The beneficiaries preferred lower level of copayment at 20 baht. The beneficiaries similarly weighed importance level on the attributes of accessibility and quantity at 22.47% and 22.38%, respectively.  Results from 330 questionnaires having coinsurance, as the cost sharing attribute, showed the beneficiaries weighed highest importance, 33.23%, on the cost sharing. The beneficiaries preferred lower level of coinsurance at 10%. The second important attribute was the formulary restriction and its relative importance was 26.05%. The beneficiaries preferred having access to drugs both listed and not listed in national essential drug list.  The beneficiaries similarly weighed importance level on the attributes of accessibility and quantity at 21.02% and 19.96%, respectively.   CONCLUSIONS:  The CSMBS beneficiaries weighed on the cost sharing and formulary attributes to be more important than the accessibility and quantity attributes when they considered drug benefit plans.