The Best-Worst Method (BWM) is a Multi-Criteria Decision Making (MCDM) method that has recently been introduced. The original BWM assumes that decision-makers are always certain about their judgments even if, in reality, decision-makers often express uncertain preferences. To deal with uncertainty, we introduce a belief structure in the BWM, a concept involving the preference degree adopted via Dempster-Shafer theory. A new approach is proposed to allow BWM to cope with this kind of information, where the level of belief in preferences being expressed is taken into account. In addition, an inconsistency measurement and an uncertainty measurement are proposed for the belief-based BWM, providing the foundation for a reliability degree of the decision-makers, after which the belief-based BWM is extended to include a group of decision-makers. Based on their reliability degrees and the weights of the criteria obtained from the various individuals, the overall criteria weights can be aggregated accordingly. Finally, a case study on the assessment of the infrastructure project criteria system in Indonesia is provided to demonstrate the applicability and feasibility of the proposed method.