With the wide spread of Internet, intelligent systems to support travel planning have been progressed during last decade. The current on-line travel support systems, however, have limits in their capabilities to adapt to the changes in travel plans. When the preferred travel plan is not available, especially during peak seasons, a traveler needs to re-plan by compromising his or her preferences, which requires time consuming and cumbersome efforts. This paper introduces an adaptive travel planning system with intelligent agent that can adapt to the dynamics of travel plans. This system consists of an adaptive travel-planning model, which is served as knowledge for agent to find alternatives and choose the best one, and a collaboration mechanism between the agents. This system provides more acceptable travel plans to travelers while reducing the risk of having no ticket in hand. The usefulness of the system is illustrated using a specific travel planning scenario. (C) 2004 Elsevier Ltd. All rights reserved.