Nowadays, software systems are more and more frequently designed in order to realize complex dynamical behavior for solving complicated problems. Holonic Multi Agent Systems (HMAS) is spreading for the development of such systems since they allow to manage system requirements in terms of behaviors and organizational patterns. Traditional software engineering metrics are not useful for measuring HMAS architectures since they do not consider different nested levels of organizational structures. We want to contribute to this issue proposing some metrics for evaluating modularity and extensibility of HMAS architectures. Categories and Subject Descriptors D.2.8 [Software Engineering]: Metrics—complexity measures General Terms Measurement Keywords Metrics; Holonic Multi Agent System; Holon