A challenging and important task in knowledge-based system development is the process of extracting, structuring, organizing and verifying knowledge elicited from domain experts, known as knowledge acquisition. In comparison with the corresponding requirement analysis process in conventional systems, knowledge acquisition lacks appropriate modeling and analysis tools. Object-oriented modeling is an emerging technique, the importance of which has only recently been recognized. We discuss here criteria for good analysis models for knowledge acquisition. Object-oriented modeling is evaluated and found sufficient to satisfy all the criteria. The advantages of an object-oriented approach are shown in a case study. Comparisons between an object-oriented approach and a conventional structure analysis approach in knowledge acquisition are included.