Dissertation (MSc Computer Science)ICT has presented a great opportunity for governments to offer better and quicker services to its citizens through e-Government platform. However, the expected goals of e-Government can only be realized if such e-Government systems are usable. Usability, which relate to user interface design aspects, play a pivotal role in the success or failure of e-Government systems. For the case of Tanzania, reports indicate low citizens’ participation in the use of e-Government systems. Several non-technical issues have been suggested but no literature was found to address technical side of usability of user interfaces for web-based e-Government systems. Hence, the main aim of this research was to investigate usability shortcomings on web-based e-Government systems in the context of Tanzania with the view of understanding its effects to users and propose the guidelines for improvement. The study used both quantitative and qualitative measures to investigate six web-based e- Government systems; five ministerial e-Government websites and Tanzania Government website. A combination of two main usability investigation methods namely user-test (UT) with thinking-aloud protocol and heuristic evaluation (HE) were used. First the e-Government systems were tested for their compliance with usability principles (heuristics). Secondly 90 users were involved in user-test with scenario based test-tasks for each e-Government Website (EGW) and records were taken as they accomplished given tasks. Results show a number of usability pitfalls which make EGWs partially usable with an overall usability score of about 43.3% and pose some difficulties for users to interact with the systems. Results from both HE and UT served as a basis for development of usability guidelines.