[EN] Usability is generally regarded as ensuring that software products are effective and efficient to use from the user's perspective. Diverse aspects that ensure the usability of a software product should be assessed during the different phases in its life cycle. The goal of usability testing is to evaluate whether or not a tool that is being developed will be usable by the end user in order to achieve the tasks for which it is being designed. This paper is targeted at describing the evaluation and the usability of OWL-VisMod, a visual modelling tool for OWL ontologies, from the point of view of the human-computer interaction. This evaluation is based on a user-centred approach and the use of questionnaires. The whole usability evaluation process is described and the results are discussed.