The usage of mobile phones and their related Internet transactional activity through mobile portals (m-portals) are an everyday activity for increasing numbers of people. However, unlike investigation of users’ attitudes to more static computing devices, user satisfaction with m-portals is yet to be researched. In addressing this gap, this research draws upon knowledge gained from Stage One of a project that used focus groups to establish the dimensions and items regarded as relevant for measuring m-portal user satisfaction. Based on this, the results from Stage Two, namely the development and validation of a multiple-item instrument for measuring user satisfaction with mportals are now reported. The theoretical contribution of this study concerns development of an instrument to measure user satisfaction in the context of m-portals. This extends knowledge in the measurement stream of Information Systems research. Moreover, through measured understanding of user attitudes to post adoption of m-portals, findings inform the m-commerce stream of research.