OBJECTIVES To examine Thai Civil Servant Medical Benefit Scheme (CSMBS) beneficiaries' preferences for attributes of drug benefit plans. METHODS Based on conjoint analysis, a self-administered questionnaire was designed to include ten hypothetical drug benefit plans which were described by four attributes e.g. patient cost sharing, formulary restrictiveness, quantity restrictiveness, and accessibility restrictiveness. Each attribute contained various levels. A total of 600 questionnaires were placed at various governmental offices in a province of southern Thailand. The respondents were asked to evaluate and determine overall preference for each plan. Part-worth utility values for each level of each attribute for each beneficiary were estimated. Importance scores for each attribute were calculated and averaged across all the beneficiaries. A segmentation analysis was also analyzed from the results of conjoint analysis. RESULTS Response rate was about 66%. Average age of the respondents was about 43 years old. Most of them were female (60.6%) and married (69.9%). More than 80% of them had either a bachelor degree or higher. Their average monthly income was about 22,832 Baht. The estimated relative importance from a conjoint analysis indicated that the cost sharing was the most important attributes (44.95% relative importance). Among the levels of cost sharing attribute, coinsurance at 25% was the most preferred choice. Formulary restrictiveness was the second most important attribute (25.54% relative importance), while the restrictions of accessibility and quantity had similar relative importance for the beneficiaries. The results from market segmentation analysis showed that almost half of the respondents considered cost sharing as the most important attribute for their preferred plan. CONCLUSIONS This study demonstrated the CSMBS beneficiaries' preferences for the attributes of drug benefit schemes. Among four studied attributes, the most important attribute that the respondents chose was cost sharing.