In order to achieve the principle of proportionality, the role in the offense shall be taken into consideration in sentencing. In Thailand, the role in the offense has recently been an aggravating factor under the new Narcotics Code. However, the new Narcotics Code could not properly differentiate offenders by culpability and reduce the harshness of the quantitybased sentencing guidelines. Neither the Supreme Court of Thailandûs holding nor the guideline related to the role in the offense has been published. As the U.S. had successfully revised the Federal Sentencing Guidelines to involve the role in the offense in sentencing, this article aims to demonstrate the construction and application of Federal Sentencing Guidelines in drug cases focusing on the role in the offense-both aggravating roles and mitigating roles. Further, this article studies important factors the court should consider when distinguishing the defendantûs role to account effectively for culpability.