The systems usability has been the subject of increasing discussion for several decades and when this concerns to computer support collaborative learning (CSCL) environment, it becomes a harder task. In CSCL environments, the usability is evaluated based on the the technical and pedagogical aspects. Therefore, the literature discusses different methods and techniques to validate usability in such environments. However, these methods usually need to be applied manually. The manual process use to be very expensive, very specific and time consuming. In addition, in CSCL environments, the usability validation becomes even more difficult due the existence of several usability requirements and its high level of interaction. For this reason, there is a need to automate the process. On the one hand, the technical usability can be automated after a formal description of the environment features. On the other hand, the pedagogical usability is dependent on the user experience and it is not possible to be totally automated. This paper presents a semi-automatic validation system to improve usability in CSCL environments. It uses ontology to represent the usability knowledge and software agents to automate the process. Finally, a case study in a real environment is described to present the advantages of using the proposed system.