s This paper introduces an architecture-centric object-oriented design method for MAS (Multi-Agent Systems) using the extended UML (Unified Modeling Language). The UML extension is based on design principles that are derived from characteristics of MAS and concept of software architecture which helps to design reusable and wellstructured multi-agent architecture. The extension allows one to use original objectoriented method without syntactic or semantic changes which implies the preservation of OO productivity, i.e., the availability of developers and tools, the utilization of past experiences and knowledge, and the seamless integration with other systems.