Automatic Ontology Building from Web Documents An Ontology represents semantics and allows interoperability between heterogeneous web documents for the same domain. Most web documents present a semi-structured organization, e.g. html, but lack explicitly defined semantics. We propose a model to analyze the unstructured and semi-structured data of web documents, with the purpose of building automatically, an ontology that represents the concepts in the contents of the documents. This model includes three phases. The first phase uses Natural Language Processing and Statistical methods to analyze the unstructured data and get important vocabulary (concepts) of the ontology. The second phase uses a Web Content Mining method to analyze the semi-structured data and find the relationships derived from the content. The last phase evaluates the concepts and relationships to determine the structure and knowledge to preserve for the ontology.