In this paper, we improve and extend the MaSE methodology to bridge the gaps in this methodology. First, we propose an improvement process and, based on this process, we report the discovered gaps and weaknesses in the methodology during different phases of case study life cycle. For removing the reported weaknesses, we introduce a "Role Schema" to document roles properties and the "Knowledge Modeling" step in order to model knowledge of each single agent in the analysis phase of methodology. We also propose an "Agent–Object model" to decrease design and implementation complexity and improve efficiency of the developed agent-based system. For evaluating the proposed refinements and extensions we have analyzed and designed the CASBA multiagent system with the improved MaSE. We will show that these improvements will increase expressiveness and refinability of the methodology and maintainability of the developed agent-based system. Categories and Subject D...