For interactions to be possible within the Service Oriented Architecture (SOA) ecosystem, each actor must be enough confident of other actors to engage safely in the interactions. Therefore, the establishing of objective metrics tailored to the context of SOA that show security of a system and lead to enhancements is very attractive. The purpose of our paper is to present a GQM (Goal Question Metric) approach based on Standard security metrics and on SOA maturity that can be a support for organizations to assess SOA Security and to ensure the safety of their SOA based collaborations