Web Portals are increasingly being used for important tasks, at a work, personal or leisure related issues. Since Web Portals provide with applications, services and information, their levels of quality are an important prerequisite for their success, and hence, a way to ensure that they do not disappear as a consequence of their not having been used. According to the ISO, there are various perspectives of quality: internal, external, and in use. Although issues related to external quality and internal quality have been widely studied in literature, we consider that it is also necessary to take account the importance of quality in use of web portals. This paper is aimed at defining a quality model to assess the level of quality in use of Web Portals. The model is founded on the ISO/IEC 25010 standard, and on some related works found in literature.