Knowledge-based decision systems support the decision analysis process with decision analytic knowledge as well as domain-specific knowledge. The knowledge in the knowledgebased decision system is usually represented by influence diagrams. In the development of knowledge-based decision systems, knowledge acquisition is one of the most difficult problems. This article suggests a knowledge acquisition process using verbal protocol analysis and multi-attribute decision-making methodology. An environmental decision-making problem is used as an illustrative example to explain the developed knowledge acquisition process. The suggested process is so flexible that it can be expanded or applied to other problems with ease. Some guidelines for the knowledge-based decision system are also suggested.