Abstract: With the increasing importance of complex software systems in the software industry, the need for using agent technologies to develop large-scale commercial and industrial software systems is growing rapidly. Such systems are complex and there is a pressing need for system modeling techniques to support reliable, maintainable and extensible design. G-Nets are a type of Petri net defined to support modeling of a system as a set of independent and loosely-coupled modules. In this paper, we first introduce an extension of G-Nets, agent-based G-Net, as a generic model for agent design. Then to progress from an agent-based design model to an agent-oriented model, new mechanisms to support inheritance modeling are introduced. To illustrate our formal modeling technique for multi-agent systems, an example of an agent family in electronic commerce is provided.