The main purpose of this study is to present an evaluation method that employs the well-established Importance-Performance Analysis (IPA) for understanding airline passengers' degree of care, degree of satisfaction and priority list on some critical service items. The analysis results will serve as the basis for airlines to improve their service strategies in response to customer needs. The proposed method has been applied in the Taiwan UNI AIR market analysis through a comprehensive passenger survey. The application results clearly indicate that the proposed IPA method can effectively identify critical airline service items to be improved, and serve as a valuable tool to assist airline managers in developing airline service improvement strategies.