Ontological models play an important role in the semantic web.Despite being widely spread,there are a few known attempst to build ontologies for the arabic language.As a result, a lack of arabic semantic web applications is encountered. In this paper,we propose an approach to build ontologies automatically for the arabic language from wikipedia.Our approach relies on the smantic field theory such that any wikipedian article is analyzed to extract semantic relations using its infobox and list of categories. We will also present our system architecture along with an initial evaluation to evaluate the effectiveness and correctness of the resultant ontological model. Keywords: Knowledge representation, ontology, relation extraction, wikipedia.