One of the important issues in port services is to evaluate the performance of the services. Without evaluating port services and their related components, these services cannot be considered desirable and its quality cannot be enhanced. However, the evaluation and the quality assurance of port services should be accomplished based on a scientific framework and a coherent framework to have desirable results. The importance-performance analysis model is an appropriate framework where each component is evaluated in terms of two dimensions of importance and performance. This study performs performance-importance analysis of ports’ services quality form perspective of containerized liner shipping in the Imam Khomeini port. In this exploratory study, 150 shipping lines experts are chosen, randomly in 2012. The study identifies 28 components of quality in port services and shipping lines’ experts are requested to evaluate these components in terms of two dimensions of importance and performance. Results reveal that there is a gap between the importance and performance of all port services components except three components of 6, 19 and 24. In addition, the results indicate that Importance-Performance Analysis (IPA) model is capable of evaluating and assuring quality in port services and can precisely identify the strengths and weaknesses of the seaport system and provide guidance for strategy formulation for quality improvement.