The concept of green manufacturing is emerging as a means of enhancing a firm's competitiveness through intelligent systems and process improvement to eliminate adverse effects on the environment. However, environmental performance (EPA) is challenging from the decision-making perspective because of difficulty determining and prioritising the proper factors that have significant effect on a firm's EPA. This study was conducted with the objective of enhancing the effectiveness of the analytic hierarchy process (AHP) to assess EPA by integrating exploratory factor analysis and confirmatory factory analysis to validate suitable criteria and sub-criteria. A questionnaire survey was employed as a tool to collect data from 341 managers of Thailand and Taiwan's food industry and the AHP approach used for normalisation, ranking, and simulation of sensitivity analysis. The results obtained indicate that quality policy, quality assurance, and quality control, respectively, are the three most important factors in the measurement of EPA, whereas organisational support in innovativeness is assigned the lowest priority. Based on simulations for sensitivity analysis, the results can be applied to guide managers' decisions in the course of steering their firms towards sustainable manufacturing.