Due to climate change and the necessity of achieving net-zero targets by 2050, sustainability is becoming increasingly important across various sectors. Globally, attention to the environmental sustainability of healthcare institutions is growing exponentially, particularly due to their impact on carbon footprints. ISO 14001 certification stands out as a potent indicator of environmental prowess, influencing the selection of suppliers with a commitment to green practices. Companies holding this certification often enjoy preference in green procurement processes. Conventional ISO 14001 audits predominantly focus on verifying a company's adherence to standard criteria, leaving unaddressed the dimension of "how well" each criterion is satisfied or the relative "importance" of individual criteria. The aim of this study is to develop an integrated approach to evaluate the green procurement performance of four companies operating in the healthcare sector and to select the best supplier, taking into account the ISO 14001:2015 criteria. The Analytic Hierarchy Process (AHP) was used to prioritize the criteria defined in the ISO 14001:2015 standard, and the Preference Ranking Organization Method for Enrichment Evaluations (PROMETHEE) was applied to rank the companies based on their compliance with these prioritized criteria. According to the research findings, the most important criteria in the environmental management system are “leadership” and “planning.” The most significant sub-criteria were identified as “leadership and commitment” and “actions to address risks and opportunities.” It is evident that companies that consider the weighted importance of ISO criteria will gain environmental benefits in terms of quality, cost, and delivery, both for themselves and for the world.