Agent oriented software development is generally motivated by the need of open and adaptive systems develpoment that continuously change and evolve to meet new requirements. In this paper, we propose an agent-based open and adaptive system development process. The proposed methodology is based on modelbased techniques and provides a specific model for the type of information to be gathered and uses this model to drive the user-oriented requirement analysis, specification and system- oriented analysis process. The proposed methodology also reduces the complexity of the software system and provides better quality with better user- satisfaction. The Gaia and ROADMAP models have been used as a fundamental ingredient to the new proposed agent-based modeling method. In the proposed agent-based system, the focus is on a clear separtion between the requirement gathering and analysis phases. The scope of the discussion covers requirements gathering and user-oriented analysis phases only and does not touch upon the systemanalysis and design phases.