In this paper, we define a set of metrics for the evaluation of conceptual models of business processes. The proposal supposes the adaptation and extension of the FMESP framework (Framework for the Modeling and Evaluation of Software Processes). This adaptation can be carried out thanks to the similarities that exist between both types of processes (software and business). FMESP includes a set of metrics, which provide the quantitative basis necessary to find out the maintainability of the software process models. This proposal has been used as the starting point in proposing a set of metrics for the evaluation of the complexity of business process models defined by BPMN (Business Process Modeling Notation). Moreover, the groups of metrics of FMESP have been extended. This is because the models of business processes represented in BPMN include quite a number of aspects of interest in this domain which are not considered in software processes modelled with SPEM (Software Process Engine...