The demand for environmental performance assessment is increasing among business practitioners, and it has nowadays become one of the key factors for a company’s self-improvement as well as for selecting suppliers and logistics providers. The assessment is, in essence, a multiple criteria decision analysis (MCDA) problem comprised of many quantitative and qualitative criteria. Frequently, the assessment data of some criterion is inevitably imprecise and/or incomplete since the nature of environmental assessment relies heavily on professional and complex methods which might not be fully available for every company. Also, qualitative criteria can only be assessed based upon human judgment. This paper, therefore, proposes an application of the evidential reasoning (ER) approach to the assessment of environmental performance for logistics service providers. The lists of criteria and indicators are adapted from ISO 14031. The ER approach is able to logically aggregate all assessment information, although different forms of data (precise or imprecise; complete or incomplete) are obtained. For this paper, assessment data from two logistics companies were gathered and analysed to illustrate the implementation process. The results are in the form of aggregated belief distributions on a unified set of evaluation grades, and the company can use this information for performance improvement and benchmarking.