Usability of software belongs today to the top priorities of both managers and users of information technologies because the dependency of the majority of mankind activities on information and communication technologies in general is increasing rapidly. This requirement concerns geographic information systems in general but it principally concerns GeoWeb sites because spatial data and tools for their utilization are nowadays in great demand by end-users. GeoWeb sites can provide them an easy-to-use solution but they must be properly designed. The article describes proposal of heuristic evaluation of usability of GeoWeb sites and a case study: the proposed heuristic evaluation is applied to GeoWeb sites of all Czech regional authorities. ISO/IEC 9126 quality model is used as a framework and heuristic evaluation in according to Nielsen is used as a method for usability inspection. In the end some recommendations how user interface should be designed are proposed.