This paper introduces an ontology-based framework to improve the preparation of ISO/IEC 27001 audits, and to strengthen the security state of the company respectively. Building on extensive previous work on security ontologies, we elaborate on how ISO/IEC 27001 artifacts can be integrated into this ontology. A basic introduction to security ontologies is given first. Specific examples show how certain ISO/IEC 27001 requirements are to be integrated into the ontology; moreover, our rule-based engine is used to query the knowledge base to check whether specific security requirements are fulfilled. The aim of this paper is to explain how security ontologies can be used for a tool to support the ISO/IEC 27001 certification, providing pivotal information for the preparation of audits and the creation and maintenance of security guidelines and policies.